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<h2 id="toc-title">Table of contents</h2>
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<li><a href="#sec-sfintro" id="toc-sec-sfintro" class="nav-link active" data-scroll-target="#sec-sfintro"><span class="header-section-number">7.1</span> Package <strong>sf</strong></a>
<ul class="collapse">
<li><a href="#creation" id="toc-creation" class="nav-link" data-scroll-target="#creation">Creation</a></li>
<li><a href="#reading-and-writing" id="toc-reading-and-writing" class="nav-link" data-scroll-target="#reading-and-writing">Reading and writing</a></li>
<li><a href="#subsetting" id="toc-subsetting" class="nav-link" data-scroll-target="#subsetting">Subsetting</a></li>
<li><a href="#binary-predicates" id="toc-binary-predicates" class="nav-link" data-scroll-target="#binary-predicates">Binary predicates</a></li>
<li><a href="#tidyverse" id="toc-tidyverse" class="nav-link" data-scroll-target="#tidyverse">tidyverse</a></li>
</ul></li>
<li><a href="#spatial-joins" id="toc-spatial-joins" class="nav-link" data-scroll-target="#spatial-joins"><span class="header-section-number">7.2</span> Spatial joins</a>
<ul class="collapse">
<li><a href="#sampling-gridding-interpolating" id="toc-sampling-gridding-interpolating" class="nav-link" data-scroll-target="#sampling-gridding-interpolating">Sampling, gridding, interpolating</a></li>
</ul></li>
<li><a href="#sec-ccw" id="toc-sec-ccw" class="nav-link" data-scroll-target="#sec-ccw"><span class="header-section-number">7.3</span> Ellipsoidal coordinates</a></li>
<li><a href="#package-stars" id="toc-package-stars" class="nav-link" data-scroll-target="#package-stars"><span class="header-section-number">7.4</span> Package <strong>stars</strong></a>
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<li><a href="#reading-and-writing-raster-data" id="toc-reading-and-writing-raster-data" class="nav-link" data-scroll-target="#reading-and-writing-raster-data">Reading and writing raster data</a></li>
<li><a href="#subsetting-stars-data-cubes" id="toc-subsetting-stars-data-cubes" class="nav-link" data-scroll-target="#subsetting-stars-data-cubes">Subsetting <code>stars</code> data cubes</a></li>
<li><a href="#cropping" id="toc-cropping" class="nav-link" data-scroll-target="#cropping">Cropping</a></li>
<li><a href="#redimensioning-and-combining-stars-objects" id="toc-redimensioning-and-combining-stars-objects" class="nav-link" data-scroll-target="#redimensioning-and-combining-stars-objects">Redimensioning and combining <code>stars</code> objects</a></li>
<li><a href="#extracting-point-samples-aggregating" id="toc-extracting-point-samples-aggregating" class="nav-link" data-scroll-target="#extracting-point-samples-aggregating">Extracting point samples, aggregating</a></li>
<li><a href="#sec-starspredict" id="toc-sec-starspredict" class="nav-link" data-scroll-target="#sec-starspredict">Predictive models</a></li>
<li><a href="#plotting-raster-data" id="toc-plotting-raster-data" class="nav-link" data-scroll-target="#plotting-raster-data">Plotting raster data</a></li>
<li><a href="#analysing-raster-data" id="toc-analysing-raster-data" class="nav-link" data-scroll-target="#analysing-raster-data">Analysing raster data</a></li>
<li><a href="#curvilinear-rasters" id="toc-curvilinear-rasters" class="nav-link" data-scroll-target="#curvilinear-rasters">Curvilinear rasters</a></li>
<li><a href="#gdal-utils" id="toc-gdal-utils" class="nav-link" data-scroll-target="#gdal-utils">GDAL utils</a></li>
</ul></li>
<li><a href="#vector-data-cube-examples" id="toc-vector-data-cube-examples" class="nav-link" data-scroll-target="#vector-data-cube-examples"><span class="header-section-number">7.5</span> Vector data cube examples</a>
<ul class="collapse">
<li><a href="#example-aggregating-air-quality-time-series" id="toc-example-aggregating-air-quality-time-series" class="nav-link" data-scroll-target="#example-aggregating-air-quality-time-series">Example: aggregating air quality time series</a></li>
<li><a href="#sec-oddc" id="toc-sec-oddc" class="nav-link" data-scroll-target="#sec-oddc">Example: Bristol origin-destination data cube</a></li>
<li><a href="#tidy-array-data" id="toc-tidy-array-data" class="nav-link" data-scroll-target="#tidy-array-data">Tidy array data</a></li>
<li><a href="#file-formats-for-vector-data-cubes" id="toc-file-formats-for-vector-data-cubes" class="nav-link" data-scroll-target="#file-formats-for-vector-data-cubes">File formats for vector data cubes</a></li>
</ul></li>
<li><a href="#sec-raster-to-vector" id="toc-sec-raster-to-vector" class="nav-link" data-scroll-target="#sec-raster-to-vector"><span class="header-section-number">7.6</span> Raster-to-vector, vector-to-raster</a>
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<li><a href="#vector-to-raster" id="toc-vector-to-raster" class="nav-link" data-scroll-target="#vector-to-raster">Vector-to-raster</a></li>
</ul></li>
<li><a href="#sec-projsf" id="toc-sec-projsf" class="nav-link" data-scroll-target="#sec-projsf"><span class="header-section-number">7.7</span> Coordinate transformations and conversions</a>
<ul class="collapse">
<li><a href="#st_crs" id="toc-st_crs" class="nav-link" data-scroll-target="#st_crs"><code>st_crs</code></a></li>
<li><a href="#st_transform-sf_project" id="toc-st_transform-sf_project" class="nav-link" data-scroll-target="#st_transform-sf_project"><code>st_transform</code>, <code>sf_project</code></a></li>
<li><a href="#sf_proj_info" id="toc-sf_proj_info" class="nav-link" data-scroll-target="#sf_proj_info"><code>sf_proj_info</code></a></li>
<li><a href="#datum-grids-proj.db-cdn.proj.org-local-cache" id="toc-datum-grids-proj.db-cdn.proj.org-local-cache" class="nav-link" data-scroll-target="#datum-grids-proj.db-cdn.proj.org-local-cache">Datum grids, proj.db, cdn.proj.org, local cache</a></li>
<li><a href="#sec-pipelines" id="toc-sec-pipelines" class="nav-link" data-scroll-target="#sec-pipelines">Transformation pipelines</a></li>
<li><a href="#sec-axisorder" id="toc-sec-axisorder" class="nav-link" data-scroll-target="#sec-axisorder">Axis order and direction</a></li>
</ul></li>
<li><a href="#sec-warp" id="toc-sec-warp" class="nav-link" data-scroll-target="#sec-warp"><span class="header-section-number">7.8</span> Transforming and warping rasters</a></li>
<li><a href="#exercises" id="toc-exercises" class="nav-link" data-scroll-target="#exercises"><span class="header-section-number">7.9</span> Exercises</a></li>
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<div class="quarto-title-block"><div><h1 class="title"><span id="sec-sf" class="quarto-section-identifier"><span class="chapter-number">7</span> <span class="chapter-title">Introduction to sf and stars</span></span></h1><button type="button" class="btn code-tools-button dropdown-toggle" id="quarto-code-tools-menu" data-bs-toggle="dropdown" aria-expanded="false"><i class="bi"></i> Code</button><ul class="dropdown-menu dropdown-menu-end" aria-labelelledby="quarto-code-tools-menu"><li><a id="quarto-show-all-code" class="dropdown-item" href="javascript:void(0)" role="button">Show All Code</a></li><li><a id="quarto-hide-all-code" class="dropdown-item" href="javascript:void(0)" role="button">Hide All Code</a></li><li><hr class="dropdown-divider"></li><li><a id="quarto-view-source" class="dropdown-item" href="javascript:void(0)" role="button">View Source</a></li></ul></div></div>
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<p></p>
<p>This chapter introduces R packages <strong>sf</strong> and <strong>stars</strong>. <strong>sf</strong> provides a table format for simple features, where feature geometries are stored in a list-column. R package <strong>stars</strong> was written to support raster and vector data cubes (<a href="06-Cubes.html"><span>Chapter 6</span></a>), supporting raster layers, raster stacks and feature time series as special cases. <strong>sf</strong> first appeared on CRAN in 2016, <strong>stars</strong> in 2018. Development of both packages received support from the R Consortium as well as strong community engagement. The packages were designed to work together. Functions or methods operating on <strong>sf</strong> or <strong>stars</strong> objects start with <code>st_</code>, making it easy to recognise them or to search for them when using command line completion.</p>
<section id="sec-sfintro" class="level2" data-number="7.1">
<h2 data-number="7.1" class="anchored" data-anchor-id="sec-sfintro"><span class="header-section-number">7.1</span> Package <strong>sf</strong></h2>
<p> </p>
<p>Intended to succeed and replace R packages <strong>sp</strong>, <strong>rgeos</strong> and the vector parts of <strong>rgdal</strong>, R package <strong>sf</strong> <span class="citation" data-cites="rjsf">(<a href="references.html#ref-rjsf" role="doc-biblioref">Pebesma 2018</a>)</span> was developed to move spatial data analysis in R closer to standards-based approaches seen in the industry and open source projects, to build upon more modern versions of the open source geospatial software stack (<a href="01-hello.html#fig-gdal-fig-nodetails">Figure <span>1.7</span></a>), and to allow for integration of R spatial software with the tidyverse <span class="citation" data-cites="welcome">(<a href="references.html#ref-welcome" role="doc-biblioref">Wickham et al. 2019</a>)</span>, if desired.</p>
<p></p>
<p>To do so, R package <strong>sf</strong> provides simple features access <span class="citation" data-cites="herring2011opengis">(<a href="references.html#ref-herring2011opengis" role="doc-biblioref">Herring et al. 2011</a>)</span>, natively, to R. It provides an interface to several <strong>tidyverse</strong> packages, in particular to <strong>ggplot2</strong>, <strong>dplyr</strong>, and <strong>tidyr</strong>. It can read and write data through GDAL, execute geometrical operations using GEOS (for projected coordinates) or s2geometry (for ellipsoidal coordinates), and carry out coordinate transformations or conversions using PROJ. External C++ libraries are interfaced using R package <strong>Rcpp</strong> <span class="citation" data-cites="eddelbuettel2013seamless">(<a href="references.html#ref-eddelbuettel2013seamless" role="doc-biblioref">Eddelbuettel 2013</a>)</span>.</p>
<p> </p>
<p>Package <strong>sf</strong> represents sets of simple features in <code>sf</code> objects, a sub-class of a <code>data.frame</code> or tibble. <code>sf</code> objects contain at least one <em>geometry list-column</em> of class <code>sfc</code>, which for each element contains the geometry as an R object of class <code>sfg</code>. A geometry list-column acts as a variable in a <code>data.frame</code> or tibble, but has a more complex structure than basic vectors such as numeric or character variables <a href="rbasics.html#sec-dissecting"><span>Section B.3</span></a>.</p>
<p> </p>
<p>An <code>sf</code> object has the following metadata:</p>
<ul>
<li>the name of the (active) geometry column, held in attribute <code>sf_column</code></li>
<li>for each non-geometry variable, the attribute-geometry relationship (<a href="05-Attributes.html#sec-agr"><span>Section 5.1</span></a>), held in attribute <code>agr</code></li>
</ul>
<p> </p>
<p></p>
<p>An <code>sfc</code> geometry list-column is extracted from an <code>sf</code> object with <code>st_geometry</code> and has the following metadata:</p>
<ul>
<li>coordinate reference system held in attribute <code>crs</code></li>
<li>bounding box held in attribute <code>bbox</code></li>
<li>precision held in attribute <code>precision</code></li>
<li>number of empty geometries held in attribute <code>n_empty</code></li>
</ul>
<p> </p>
<p>These attributes may best be accessed or set by using functions like <code>st_bbox</code>, <code>st_crs</code>, <code>st_set_crs</code>, <code>st_agr</code>, <code>st_set_agr</code>, <code>st_precision</code>, and <code>st_set_precision</code>.</p>
<p>Geometry columns in <code>sf</code> objects can be set or replaced using <code>st_geometry<-</code> or <code>st_set_geometry</code>.</p>
<section id="creation" class="level3">
<h3 class="anchored" data-anchor-id="creation">Creation</h3>
<p>An <code>sf</code> object can be created from scratch by</p>
<p></p>
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<div class="sourceCode cell-code" id="cb1"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="fu">library</span>(sf)</span>
<span id="cb1-2"><a href="#cb1-2" aria-hidden="true" tabindex="-1"></a><span class="co"># Linking to GEOS 3.11.1, GDAL 3.6.2, PROJ 9.1.1; sf_use_s2() is TRUE</span></span>
<span id="cb1-3"><a href="#cb1-3" aria-hidden="true" tabindex="-1"></a>p1 <span class="ot"><-</span> <span class="fu">st_point</span>(<span class="fu">c</span>(<span class="fl">7.35</span>, <span class="fl">52.42</span>))</span>
<span id="cb1-4"><a href="#cb1-4" aria-hidden="true" tabindex="-1"></a>p2 <span class="ot"><-</span> <span class="fu">st_point</span>(<span class="fu">c</span>(<span class="fl">7.22</span>, <span class="fl">52.18</span>))</span>
<span id="cb1-5"><a href="#cb1-5" aria-hidden="true" tabindex="-1"></a>p3 <span class="ot"><-</span> <span class="fu">st_point</span>(<span class="fu">c</span>(<span class="fl">7.44</span>, <span class="fl">52.19</span>))</span>
<span id="cb1-6"><a href="#cb1-6" aria-hidden="true" tabindex="-1"></a>sfc <span class="ot"><-</span> <span class="fu">st_sfc</span>(<span class="fu">list</span>(p1, p2, p3), <span class="at">crs =</span> <span class="st">'OGC:CRS84'</span>)</span>
<span id="cb1-7"><a href="#cb1-7" aria-hidden="true" tabindex="-1"></a><span class="fu">st_sf</span>(<span class="at">elev =</span> <span class="fu">c</span>(<span class="fl">33.2</span>, <span class="fl">52.1</span>, <span class="fl">81.2</span>), </span>
<span id="cb1-8"><a href="#cb1-8" aria-hidden="true" tabindex="-1"></a> <span class="at">marker =</span> <span class="fu">c</span>(<span class="st">"Id01"</span>, <span class="st">"Id02"</span>, <span class="st">"Id03"</span>), <span class="at">geom =</span> sfc)</span>
<span id="cb1-9"><a href="#cb1-9" aria-hidden="true" tabindex="-1"></a><span class="co"># Simple feature collection with 3 features and 2 fields</span></span>
<span id="cb1-10"><a href="#cb1-10" aria-hidden="true" tabindex="-1"></a><span class="co"># Geometry type: POINT</span></span>
<span id="cb1-11"><a href="#cb1-11" aria-hidden="true" tabindex="-1"></a><span class="co"># Dimension: XY</span></span>
<span id="cb1-12"><a href="#cb1-12" aria-hidden="true" tabindex="-1"></a><span class="co"># Bounding box: xmin: 7.22 ymin: 52.2 xmax: 7.44 ymax: 52.4</span></span>
<span id="cb1-13"><a href="#cb1-13" aria-hidden="true" tabindex="-1"></a><span class="co"># Geodetic CRS: WGS 84</span></span>
<span id="cb1-14"><a href="#cb1-14" aria-hidden="true" tabindex="-1"></a><span class="co"># elev marker geom</span></span>
<span id="cb1-15"><a href="#cb1-15" aria-hidden="true" tabindex="-1"></a><span class="co"># 1 33.2 Id01 POINT (7.35 52.4)</span></span>
<span id="cb1-16"><a href="#cb1-16" aria-hidden="true" tabindex="-1"></a><span class="co"># 2 52.1 Id02 POINT (7.22 52.2)</span></span>
<span id="cb1-17"><a href="#cb1-17" aria-hidden="true" tabindex="-1"></a><span class="co"># 3 81.2 Id03 POINT (7.44 52.2)</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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<div class="sourceCode cell-code" id="cb2"><pre class="sourceCode python code-with-copy"><code class="sourceCode python"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="im">import</span> geopandas <span class="im">as</span> gpd</span>
<span id="cb2-2"><a href="#cb2-2" aria-hidden="true" tabindex="-1"></a><span class="im">from</span> shapely.geometry <span class="im">import</span> Point</span>
<span id="cb2-3"><a href="#cb2-3" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-4"><a href="#cb2-4" aria-hidden="true" tabindex="-1"></a>p1 <span class="op">=</span> Point(<span class="fl">7.35</span>, <span class="fl">52.42</span>)</span>
<span id="cb2-5"><a href="#cb2-5" aria-hidden="true" tabindex="-1"></a>p2 <span class="op">=</span> Point(<span class="fl">7.22</span>, <span class="fl">52.18</span>)</span>
<span id="cb2-6"><a href="#cb2-6" aria-hidden="true" tabindex="-1"></a>p3 <span class="op">=</span> Point(<span class="fl">7.44</span>, <span class="fl">52.19</span>)</span>
<span id="cb2-7"><a href="#cb2-7" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-8"><a href="#cb2-8" aria-hidden="true" tabindex="-1"></a>gdf <span class="op">=</span> gpd.GeoDataFrame(</span>
<span id="cb2-9"><a href="#cb2-9" aria-hidden="true" tabindex="-1"></a> {<span class="st">'elev'</span>: [<span class="fl">33.2</span>, <span class="fl">52.1</span>, <span class="fl">81.2</span>], <span class="st">'marker'</span>: [<span class="st">"Id01"</span>, <span class="st">"Id02"</span>, <span class="st">"Id03"</span>]},</span>
<span id="cb2-10"><a href="#cb2-10" aria-hidden="true" tabindex="-1"></a> geometry<span class="op">=</span>[p1, p2, p3],</span>
<span id="cb2-11"><a href="#cb2-11" aria-hidden="true" tabindex="-1"></a> crs<span class="op">=</span><span class="st">'OGC:CRS84'</span></span>
<span id="cb2-12"><a href="#cb2-12" aria-hidden="true" tabindex="-1"></a>)</span>
<span id="cb2-13"><a href="#cb2-13" aria-hidden="true" tabindex="-1"></a><span class="bu">print</span>(gdf)</span>
<span id="cb2-14"><a href="#cb2-14" aria-hidden="true" tabindex="-1"></a><span class="co"># elev marker geometry</span></span>
<span id="cb2-15"><a href="#cb2-15" aria-hidden="true" tabindex="-1"></a><span class="co"># 0 33.2 Id01 POINT (7.35000 52.42000)</span></span>
<span id="cb2-16"><a href="#cb2-16" aria-hidden="true" tabindex="-1"></a><span class="co"># 1 52.1 Id02 POINT (7.22000 52.18000)</span></span>
<span id="cb2-17"><a href="#cb2-17" aria-hidden="true" tabindex="-1"></a><span class="co"># 2 81.2 Id03 POINT (7.44000 52.19000)</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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<figure class="figure">
<p><img src="images/sf_obj.png" class="img-fluid figure-img" style="width:100.0%"></p>
<figcaption class="figure-caption">Figure 7.1: components of an <code>sf</code> object</figcaption>
</figure>
</div>
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</div>
<p><a href="#fig-sfobj">Figure <span>7.1</span></a> gives an explanation of the components printed. Rather than creating objects from scratch, spatial data in R are typically read from an external source, which can be:</p>
<p></p>
<ul>
<li>external file</li>
<li>table (or set of tables) in a database</li>
<li>request to a web service</li>
<li>dataset held in some form in another R package</li>
</ul>
<p>The next section introduces reading from files. <a href="09-Large.html#sec-largesf"><span>Section 9.1</span></a> discusses handling of datasets too large to fit into working memory.</p>
</section>
<section id="reading-and-writing" class="level3">
<h3 class="anchored" data-anchor-id="reading-and-writing">Reading and writing</h3>
<p>Reading datasets from an external “data source” (file, web service, or even string) is done using <code>st_read</code>:</p>
<p></p>
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<div class="sourceCode cell-code" id="cb3"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb3-1"><a href="#cb3-1" aria-hidden="true" tabindex="-1"></a><span class="fu">library</span>(sf)</span>
<span id="cb3-2"><a href="#cb3-2" aria-hidden="true" tabindex="-1"></a>(file <span class="ot"><-</span> <span class="fu">system.file</span>(<span class="st">"gpkg/nc.gpkg"</span>, <span class="at">package =</span> <span class="st">"sf"</span>))</span>
<span id="cb3-3"><a href="#cb3-3" aria-hidden="true" tabindex="-1"></a><span class="co"># [1] "/home/edzer/R/x86_64-pc-linux-gnu-library/4.3/sf/gpkg/nc.gpkg"</span></span>
<span id="cb3-4"><a href="#cb3-4" aria-hidden="true" tabindex="-1"></a>nc <span class="ot"><-</span> <span class="fu">st_read</span>(file)</span>
<span id="cb3-5"><a href="#cb3-5" aria-hidden="true" tabindex="-1"></a><span class="co"># Reading layer `nc.gpkg' from data source </span></span>
<span id="cb3-6"><a href="#cb3-6" aria-hidden="true" tabindex="-1"></a><span class="co"># `/home/edzer/R/x86_64-pc-linux-gnu-library/4.3/sf/gpkg/nc.gpkg' </span></span>
<span id="cb3-7"><a href="#cb3-7" aria-hidden="true" tabindex="-1"></a><span class="co"># using driver `GPKG'</span></span>
<span id="cb3-8"><a href="#cb3-8" aria-hidden="true" tabindex="-1"></a><span class="co"># Simple feature collection with 100 features and 14 fields</span></span>
<span id="cb3-9"><a href="#cb3-9" aria-hidden="true" tabindex="-1"></a><span class="co"># Geometry type: MULTIPOLYGON</span></span>
<span id="cb3-10"><a href="#cb3-10" aria-hidden="true" tabindex="-1"></a><span class="co"># Dimension: XY</span></span>
<span id="cb3-11"><a href="#cb3-11" aria-hidden="true" tabindex="-1"></a><span class="co"># Bounding box: xmin: -84.3 ymin: 33.9 xmax: -75.5 ymax: 36.6</span></span>
<span id="cb3-12"><a href="#cb3-12" aria-hidden="true" tabindex="-1"></a><span class="co"># Geodetic CRS: NAD27</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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<div class="sourceCode cell-code" id="cb4"><pre class="sourceCode python code-with-copy"><code class="sourceCode python"><span id="cb4-1"><a href="#cb4-1" aria-hidden="true" tabindex="-1"></a><span class="im">import</span> geopandas <span class="im">as</span> gpd</span>
<span id="cb4-2"><a href="#cb4-2" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb4-3"><a href="#cb4-3" aria-hidden="true" tabindex="-1"></a>nc <span class="op">=</span> gpd.read_file(<span class="st">"https://github.com/r-spatial/sf/raw/main/inst/gpkg/nc.gpkg"</span>)</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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<p>Here, the file name and path <code>file</code> is read from the <strong>sf</strong> package, which has a different path on every machine, and hence is guaranteed to be present on every <strong>sf</strong> installation.</p>
<p></p>
<p>Command <code>st_read</code> has two arguments: the <em>data source name</em> (<code>dsn</code>) and the <em>layer</em>. In the example above, the <em>geopackage</em> (GPKG) file contains only a single layer that is being read. If it had contained multiple layers, then the first layer would have been read and a warning would have been emitted. The available layers of a dataset can be queried by</p>
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<div class="sourceCode cell-code" id="cb5"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb5-1"><a href="#cb5-1" aria-hidden="true" tabindex="-1"></a><span class="fu">st_layers</span>(file)</span>
<span id="cb5-2"><a href="#cb5-2" aria-hidden="true" tabindex="-1"></a><span class="co"># Driver: GPKG </span></span>
<span id="cb5-3"><a href="#cb5-3" aria-hidden="true" tabindex="-1"></a><span class="co"># Available layers:</span></span>
<span id="cb5-4"><a href="#cb5-4" aria-hidden="true" tabindex="-1"></a><span class="co"># layer_name geometry_type features fields crs_name</span></span>
<span id="cb5-5"><a href="#cb5-5" aria-hidden="true" tabindex="-1"></a><span class="co"># 1 nc.gpkg Multi Polygon 100 14 NAD27</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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<p>Simple feature objects can be written with <code>st_write</code>, as in</p>
<div class="cell">
<div class="sourceCode cell-code" id="cb6"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb6-1"><a href="#cb6-1" aria-hidden="true" tabindex="-1"></a>(<span class="at">file =</span> <span class="fu">tempfile</span>(<span class="at">fileext =</span> <span class="st">".gpkg"</span>))</span>
<span id="cb6-2"><a href="#cb6-2" aria-hidden="true" tabindex="-1"></a><span class="co"># [1] "/tmp/Rtmp7fOaVK/file21c601e2b81d7.gpkg"</span></span>
<span id="cb6-3"><a href="#cb6-3" aria-hidden="true" tabindex="-1"></a><span class="fu">st_write</span>(nc, file, <span class="at">layer =</span> <span class="st">"layer_nc"</span>)</span>
<span id="cb6-4"><a href="#cb6-4" aria-hidden="true" tabindex="-1"></a><span class="co"># Writing layer `layer_nc' to data source </span></span>
<span id="cb6-5"><a href="#cb6-5" aria-hidden="true" tabindex="-1"></a><span class="co"># `/tmp/Rtmp7fOaVK/file21c601e2b81d7.gpkg' using driver `GPKG'</span></span>
<span id="cb6-6"><a href="#cb6-6" aria-hidden="true" tabindex="-1"></a><span class="co"># Writing 100 features with 14 fields and geometry type Multi Polygon.</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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<p>where the file format (GPKG) is derived from the file name extension. Using argument <code>append</code>, <code>st_write</code> can either append records to an existing layer or replace it; if unset, it will err if a layer already exists. The tidyverse-style <code>write_sf</code> will replace silently if <code>append</code> has not been set. Layers can also be deleted using <code>st_delete</code>, which is convenient in particular when they are associated with tables in a database.</p>
<p>For file formats supporting a WKT2 coordinate reference system, <code>sf_read</code> and <code>sf_write</code> will read and write it. For simple formats such as <code>csv</code> this will not work. The shapefile format supports only a very limited encoding of the CRS.</p>
<p> </p>
</section>
<section id="subsetting" class="level3">
<h3 class="anchored" data-anchor-id="subsetting">Subsetting</h3>
<p> </p>
<p>A very common operation is to subset objects; base R can use <code>[</code> for this. The rules that apply to <code>data.frame</code> objects also apply to <code>sf</code> objects: records 2-5 and columns 3-7 are selected by</p>
<div class="cell">
<div class="sourceCode cell-code" id="cb7"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb7-1"><a href="#cb7-1" aria-hidden="true" tabindex="-1"></a>nc[<span class="dv">2</span><span class="sc">:</span><span class="dv">5</span>, <span class="dv">3</span><span class="sc">:</span><span class="dv">7</span>]</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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<p>but with a few additional features, in particular:</p>
<ul>
<li>the <code>drop</code> argument is by default <code>FALSE</code> meaning that the geometry column is <em>always</em> selected, and an <code>sf</code> object is returned; when it is set to <code>TRUE</code> and the geometry column is <em>not</em> selected, it is dropped and a <code>data.frame</code> is returned</li>
<li>selection with a spatial (<code>sf</code>, <code>sfc</code> or <code>sfg</code>) object as first argument leads to selection of the features that spatially <em>intersect</em> with that object (see next section); other predicates than <em>intersects</em> can be chosen by setting parameter <code>op</code> to a function such as <code>st_covers</code> or any other binary predicate function listed in <a href="03-Geometries.html#sec-de9im"><span>Section 3.2.2</span></a>.</li>
</ul>
</section>
<section id="binary-predicates" class="level3">
<h3 class="anchored" data-anchor-id="binary-predicates">Binary predicates</h3>
<p></p>
<p>Binary predicates like <code>st_intersects</code>, <code>st_covers</code> and such (<a href="03-Geometries.html#sec-de9im"><span>Section 3.2.2</span></a>) take two sets of features or feature geometries and return for all pairs whether the predicate is <code>TRUE</code> or <code>FALSE</code>. For large sets this would potentially result in a huge matrix, typically filled mostly with <code>FALSE</code> values and for that reason a sparse representation is returned by default:</p>
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<div class="sourceCode cell-code" id="cb8"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb8-1"><a href="#cb8-1" aria-hidden="true" tabindex="-1"></a>nc5 <span class="ot"><-</span> nc[<span class="dv">1</span><span class="sc">:</span><span class="dv">5</span>, ]</span>
<span id="cb8-2"><a href="#cb8-2" aria-hidden="true" tabindex="-1"></a>nc7 <span class="ot"><-</span> nc[<span class="dv">1</span><span class="sc">:</span><span class="dv">7</span>, ]</span>
<span id="cb8-3"><a href="#cb8-3" aria-hidden="true" tabindex="-1"></a>(i <span class="ot"><-</span> <span class="fu">st_intersects</span>(nc5, nc7))</span>
<span id="cb8-4"><a href="#cb8-4" aria-hidden="true" tabindex="-1"></a><span class="co"># Sparse geometry binary predicate list of length 5, where the</span></span>
<span id="cb8-5"><a href="#cb8-5" aria-hidden="true" tabindex="-1"></a><span class="co"># predicate was `intersects'</span></span>
<span id="cb8-6"><a href="#cb8-6" aria-hidden="true" tabindex="-1"></a><span class="co"># 1: 1, 2</span></span>
<span id="cb8-7"><a href="#cb8-7" aria-hidden="true" tabindex="-1"></a><span class="co"># 2: 1, 2, 3</span></span>
<span id="cb8-8"><a href="#cb8-8" aria-hidden="true" tabindex="-1"></a><span class="co"># 3: 2, 3</span></span>
<span id="cb8-9"><a href="#cb8-9" aria-hidden="true" tabindex="-1"></a><span class="co"># 4: 4, 7</span></span>
<span id="cb8-10"><a href="#cb8-10" aria-hidden="true" tabindex="-1"></a><span class="co"># 5: 5, 6</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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<div class="sourceCode cell-code" id="cb9"><pre class="sourceCode python code-with-copy"><code class="sourceCode python"><span id="cb9-1"><a href="#cb9-1" aria-hidden="true" tabindex="-1"></a><span class="im">import</span> geopandas <span class="im">as</span> gpd</span>
<span id="cb9-2"><a href="#cb9-2" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb9-3"><a href="#cb9-3" aria-hidden="true" tabindex="-1"></a>nc <span class="op">=</span> gpd.read_file(<span class="st">"https://github.com/r-spatial/sf/raw/main/inst/gpkg/nc.gpkg"</span>)</span>
<span id="cb9-4"><a href="#cb9-4" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb9-5"><a href="#cb9-5" aria-hidden="true" tabindex="-1"></a>nc5 <span class="op">=</span> nc[:<span class="dv">5</span>]</span>
<span id="cb9-6"><a href="#cb9-6" aria-hidden="true" tabindex="-1"></a>nc7 <span class="op">=</span> nc[:<span class="dv">7</span>]</span>
<span id="cb9-7"><a href="#cb9-7" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb9-8"><a href="#cb9-8" aria-hidden="true" tabindex="-1"></a>i <span class="op">=</span> nc5.intersects(nc7)</span>
<span id="cb9-9"><a href="#cb9-9" aria-hidden="true" tabindex="-1"></a><span class="co"># /home/edzer/.local/lib/python3.10/site-packages/geopandas/base.py:31: UserWarning: The indices of the two GeoSeries are different.</span></span>
<span id="cb9-10"><a href="#cb9-10" aria-hidden="true" tabindex="-1"></a><span class="co"># warn("The indices of the two GeoSeries are different.")</span></span>
<span id="cb9-11"><a href="#cb9-11" aria-hidden="true" tabindex="-1"></a>i</span>
<span id="cb9-12"><a href="#cb9-12" aria-hidden="true" tabindex="-1"></a><span class="co"># 0 True</span></span>
<span id="cb9-13"><a href="#cb9-13" aria-hidden="true" tabindex="-1"></a><span class="co"># 1 True</span></span>
<span id="cb9-14"><a href="#cb9-14" aria-hidden="true" tabindex="-1"></a><span class="co"># 2 True</span></span>
<span id="cb9-15"><a href="#cb9-15" aria-hidden="true" tabindex="-1"></a><span class="co"># 3 True</span></span>
<span id="cb9-16"><a href="#cb9-16" aria-hidden="true" tabindex="-1"></a><span class="co"># 4 True</span></span>
<span id="cb9-17"><a href="#cb9-17" aria-hidden="true" tabindex="-1"></a><span class="co"># 5 False</span></span>
<span id="cb9-18"><a href="#cb9-18" aria-hidden="true" tabindex="-1"></a><span class="co"># 6 False</span></span>
<span id="cb9-19"><a href="#cb9-19" aria-hidden="true" tabindex="-1"></a><span class="co"># dtype: bool</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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<div class="sourceCode cell-code" id="cb10"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb10-1"><a href="#cb10-1" aria-hidden="true" tabindex="-1"></a><span class="fu">plot</span>(<span class="fu">st_geometry</span>(nc7))</span>
<span id="cb10-2"><a href="#cb10-2" aria-hidden="true" tabindex="-1"></a><span class="fu">plot</span>(<span class="fu">st_geometry</span>(nc5), <span class="at">add =</span> <span class="cn">TRUE</span>, <span class="at">border =</span> <span class="st">"brown"</span>)</span>
<span id="cb10-3"><a href="#cb10-3" aria-hidden="true" tabindex="-1"></a>cc <span class="ot">=</span> <span class="fu">st_coordinates</span>(<span class="fu">st_centroid</span>(<span class="fu">st_geometry</span>(nc7)))</span>
<span id="cb10-4"><a href="#cb10-4" aria-hidden="true" tabindex="-1"></a><span class="fu">text</span>(cc, <span class="at">labels =</span> <span class="dv">1</span><span class="sc">:</span><span class="fu">nrow</span>(nc7), <span class="at">col =</span> <span class="st">"blue"</span>)</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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<p><img src="07-Introsf_files/figure-html/fig-fig57-1.png" class="img-fluid figure-img" style="width:100.0%"></p>
<figcaption class="figure-caption">Figure 7.2: First seven North Carolina counties</figcaption>
</figure>
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<div class="sourceCode cell-code" id="cb11"><pre class="sourceCode python code-with-copy"><code class="sourceCode python"><span id="cb11-1"><a href="#cb11-1" aria-hidden="true" tabindex="-1"></a><span class="im">import</span> matplotlib.pyplot <span class="im">as</span> plt</span>
<span id="cb11-2"><a href="#cb11-2" aria-hidden="true" tabindex="-1"></a><span class="im">import</span> geopandas <span class="im">as</span> gpd</span>
<span id="cb11-3"><a href="#cb11-3" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb11-4"><a href="#cb11-4" aria-hidden="true" tabindex="-1"></a>nc <span class="op">=</span> gpd.read_file(<span class="st">"https://github.com/r-spatial/sf/raw/main/inst/gpkg/nc.gpkg"</span>)</span>
<span id="cb11-5"><a href="#cb11-5" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb11-6"><a href="#cb11-6" aria-hidden="true" tabindex="-1"></a>nc5 <span class="op">=</span> nc[:<span class="dv">5</span>]</span>
<span id="cb11-7"><a href="#cb11-7" aria-hidden="true" tabindex="-1"></a>nc7 <span class="op">=</span> nc[:<span class="dv">7</span>]</span>
<span id="cb11-8"><a href="#cb11-8" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb11-9"><a href="#cb11-9" aria-hidden="true" tabindex="-1"></a>i <span class="op">=</span> nc5.intersects(nc7)</span>
<span id="cb11-10"><a href="#cb11-10" aria-hidden="true" tabindex="-1"></a><span class="co"># /home/edzer/.local/lib/python3.10/site-packages/geopandas/base.py:31: UserWarning: The indices of the two GeoSeries are different.</span></span>
<span id="cb11-11"><a href="#cb11-11" aria-hidden="true" tabindex="-1"></a><span class="co"># warn("The indices of the two GeoSeries are different.")</span></span>
<span id="cb11-12"><a href="#cb11-12" aria-hidden="true" tabindex="-1"></a>ax <span class="op">=</span> nc7.plot()</span>
<span id="cb11-13"><a href="#cb11-13" aria-hidden="true" tabindex="-1"></a>nc5.plot(ax<span class="op">=</span>ax, color<span class="op">=</span><span class="st">'brown'</span>)</span>
<span id="cb11-14"><a href="#cb11-14" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb11-15"><a href="#cb11-15" aria-hidden="true" tabindex="-1"></a><span class="cf">for</span> x, y, label <span class="kw">in</span> <span class="bu">zip</span>(nc7.geometry.centroid.x, nc7.geometry.centroid.y, nc7.index):</span>
<span id="cb11-16"><a href="#cb11-16" aria-hidden="true" tabindex="-1"></a> plt.text(x, y, label, fontsize<span class="op">=</span><span class="dv">12</span>)</span>
<span id="cb11-17"><a href="#cb11-17" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb11-18"><a href="#cb11-18" aria-hidden="true" tabindex="-1"></a>plt.axis(<span class="va">False</span>) </span>
<span id="cb11-19"><a href="#cb11-19" aria-hidden="true" tabindex="-1"></a><span class="co"># (-82.03946952819824, -75.47475929260254, 36.04697723388672, 36.61549072265625)</span></span>
<span id="cb11-20"><a href="#cb11-20" aria-hidden="true" tabindex="-1"></a>plt.show()</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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<p><img src="07-Introsf_files/figure-html/unnamed-chunk-9-1.png" class="img-fluid figure-img" style="width:100.0%"></p>
<figcaption class="figure-caption">First seven North Carolina counties</figcaption>
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<p><a href="#fig-fig57">Figure <span>7.2</span></a> shows how the intersections of the first five with the first seven counties can be understood. We can transform the sparse logical matrix into a dense matrix by</p>
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<span id="cb12-2"><a href="#cb12-2" aria-hidden="true" tabindex="-1"></a><span class="co"># [,1] [,2] [,3] [,4] [,5] [,6] [,7]</span></span>
<span id="cb12-3"><a href="#cb12-3" aria-hidden="true" tabindex="-1"></a><span class="co"># [1,] TRUE TRUE FALSE FALSE FALSE FALSE FALSE</span></span>
<span id="cb12-4"><a href="#cb12-4" aria-hidden="true" tabindex="-1"></a><span class="co"># [2,] TRUE TRUE TRUE FALSE FALSE FALSE FALSE</span></span>
<span id="cb12-5"><a href="#cb12-5" aria-hidden="true" tabindex="-1"></a><span class="co"># [3,] FALSE TRUE TRUE FALSE FALSE FALSE FALSE</span></span>
<span id="cb12-6"><a href="#cb12-6" aria-hidden="true" tabindex="-1"></a><span class="co"># [4,] FALSE FALSE FALSE TRUE FALSE FALSE TRUE</span></span>
<span id="cb12-7"><a href="#cb12-7" aria-hidden="true" tabindex="-1"></a><span class="co"># [5,] FALSE FALSE FALSE FALSE TRUE TRUE FALSE</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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<div class="sourceCode cell-code" id="cb13"><pre class="sourceCode python code-with-copy"><code class="sourceCode python"><span id="cb13-1"><a href="#cb13-1" aria-hidden="true" tabindex="-1"></a><span class="im">import</span> numpy <span class="im">as</span> np</span>
<span id="cb13-2"><a href="#cb13-2" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb13-3"><a href="#cb13-3" aria-hidden="true" tabindex="-1"></a>matrix <span class="op">=</span> np.matrix(i.values)</span>
<span id="cb13-4"><a href="#cb13-4" aria-hidden="true" tabindex="-1"></a>matrix</span>
<span id="cb13-5"><a href="#cb13-5" aria-hidden="true" tabindex="-1"></a><span class="co"># matrix([[ True, True, True, True, True, False, False]])</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
</div>
</div>
</div>
</div>
<p>The number of counties that each of <code>nc5</code> intersects with is</p>
<div class="cell">
<div class="sourceCode cell-code" id="cb14"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb14-1"><a href="#cb14-1" aria-hidden="true" tabindex="-1"></a><span class="fu">lengths</span>(i)</span>
<span id="cb14-2"><a href="#cb14-2" aria-hidden="true" tabindex="-1"></a><span class="co"># [1] 2 3 2 2 2</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
</div>
<p>and the other way around, the number of counties in <code>nc5</code> that intersect with each of the counties in <code>nc7</code> is</p>
<div class="cell">
<div class="sourceCode cell-code" id="cb15"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb15-1"><a href="#cb15-1" aria-hidden="true" tabindex="-1"></a><span class="fu">lengths</span>(<span class="fu">t</span>(i))</span>
<span id="cb15-2"><a href="#cb15-2" aria-hidden="true" tabindex="-1"></a><span class="co"># [1] 2 3 2 1 1 1 1</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
</div>
<p>The object <code>i</code> is of class <code>sgbp</code> (sparse geometrical binary predicate), and is a list of integer vectors, with each element representing a row in the logical predicate matrix holding the column indices of the <code>TRUE</code> values for that row. It further holds some metadata like the predicate used, and the total number of columns. Methods available for <code>sgbp</code> objects include</p>
<div class="cell">
<div class="sourceCode cell-code" id="cb16"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb16-1"><a href="#cb16-1" aria-hidden="true" tabindex="-1"></a><span class="fu">methods</span>(<span class="at">class =</span> <span class="st">"sgbp"</span>)</span>
<span id="cb16-2"><a href="#cb16-2" aria-hidden="true" tabindex="-1"></a><span class="co"># [1] as.data.frame as.matrix coerce dim </span></span>
<span id="cb16-3"><a href="#cb16-3" aria-hidden="true" tabindex="-1"></a><span class="co"># [5] initialize Ops print show </span></span>
<span id="cb16-4"><a href="#cb16-4" aria-hidden="true" tabindex="-1"></a><span class="co"># [9] slotsFromS3 t </span></span>
<span id="cb16-5"><a href="#cb16-5" aria-hidden="true" tabindex="-1"></a><span class="co"># see '?methods' for accessing help and source code</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
</div>
<p>where the only <code>Ops</code> method available is <code>!</code>, the negation operation.</p>
</section>
<section id="tidyverse" class="level3">
<h3 class="anchored" data-anchor-id="tidyverse">tidyverse</h3>
<p> </p>
<p>The <strong>tidyverse</strong> package loads a collection of data science packages that work well together <span class="citation" data-cites="r4ds welcome">(<a href="references.html#ref-r4ds" role="doc-biblioref">Wickham and Grolemund 2017</a>; <a href="references.html#ref-welcome" role="doc-biblioref">Wickham et al. 2019</a>)</span>. Package <strong>sf</strong> has <strong>tidyverse</strong>-style read and write functions, <code>read_sf</code> and <code>write_sf</code> that</p>
<ul>
<li>return a tibble rather than a <code>data.frame</code>,</li>
<li>do not print any output, and</li>
<li>overwrite existing data by default.</li>
</ul>
<p>Further <strong>tidyverse</strong> generics with methods for <code>sf</code> objects include <code>filter</code>, <code>select</code>, <code>group_by</code>, <code>ungroup</code>, <code>mutate</code>, <code>transmute</code>, <code>rowwise</code>, <code>rename</code>, <code>slice</code>, <code>summarise</code>, <code>distinct</code>, <code>gather</code>, <code>pivot_longer</code>, <code>spread</code>, <code>nest</code>, <code>unnest</code>, <code>unite</code>, <code>separate</code>, <code>separate_rows</code>, <code>sample_n</code>, and <code>sample_frac</code>. Most of these methods simply manage the metadata of <code>sf</code> objects and make sure the geometry remains present. In case a user wants the geometry to be removed, one can use <code>st_drop_geometry</code> or simply coerce to a <code>tibble</code> or <code>data.frame</code> before selecting:</p>
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<div class="cell">
<div class="sourceCode cell-code" id="cb17"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb17-1"><a href="#cb17-1" aria-hidden="true" tabindex="-1"></a><span class="fu">library</span>(tidyverse) <span class="sc">|></span> <span class="fu">suppressPackageStartupMessages</span>()</span>
<span id="cb17-2"><a href="#cb17-2" aria-hidden="true" tabindex="-1"></a>nc <span class="sc">|></span> <span class="fu">as_tibble</span>() <span class="sc">|></span> <span class="fu">select</span>(BIR74) <span class="sc">|></span> <span class="fu">head</span>(<span class="dv">3</span>)</span>
<span id="cb17-3"><a href="#cb17-3" aria-hidden="true" tabindex="-1"></a><span class="co"># # A tibble: 3 × 1</span></span>
<span id="cb17-4"><a href="#cb17-4" aria-hidden="true" tabindex="-1"></a><span class="co"># BIR74</span></span>
<span id="cb17-5"><a href="#cb17-5" aria-hidden="true" tabindex="-1"></a><span class="co"># <dbl></span></span>
<span id="cb17-6"><a href="#cb17-6" aria-hidden="true" tabindex="-1"></a><span class="co"># 1 1091</span></span>
<span id="cb17-7"><a href="#cb17-7" aria-hidden="true" tabindex="-1"></a><span class="co"># 2 487</span></span>
<span id="cb17-8"><a href="#cb17-8" aria-hidden="true" tabindex="-1"></a><span class="co"># 3 3188</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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</div>
<div id="tabset-6-2" class="tab-pane" role="tabpanel" aria-labelledby="tabset-6-2-tab">
<div class="cell">
<div class="sourceCode cell-code" id="cb18"><pre class="sourceCode python code-with-copy"><code class="sourceCode python"><span id="cb18-1"><a href="#cb18-1" aria-hidden="true" tabindex="-1"></a>nc[[<span class="st">'BIR74'</span>]].head(<span class="dv">3</span>)</span>
<span id="cb18-2"><a href="#cb18-2" aria-hidden="true" tabindex="-1"></a><span class="co"># BIR74</span></span>
<span id="cb18-3"><a href="#cb18-3" aria-hidden="true" tabindex="-1"></a><span class="co"># 0 1091.0</span></span>
<span id="cb18-4"><a href="#cb18-4" aria-hidden="true" tabindex="-1"></a><span class="co"># 1 487.0</span></span>
<span id="cb18-5"><a href="#cb18-5" aria-hidden="true" tabindex="-1"></a><span class="co"># 2 3188.0</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
</div>
</div>
</div>
</div>
<p></p>
<p>The <code>summarise</code> method for <code>sf</code> objects has two special arguments:</p>
<ul>
<li><code>do_union</code> (default <code>TRUE</code>) determines whether grouped geometries are unioned on return, so that they form a valid geometry</li>
<li><code>is_coverage</code> (default <code>FALSE</code>) in case the geometries grouped form a coverage (do not have overlaps), setting this to <code>TRUE</code> speeds up the unioning</li>
</ul>
<p>The <code>distinct</code> method selects distinct records, where <code>st_equals</code> is used to evaluate distinctness of geometries.</p>
<p><code>filter</code> can be used with the usual predicates; when one wants to use it with a spatial predicate, for instance to select all counties less than 50 km away from Orange County, one could use</p>
<div class="cell">
<div class="sourceCode cell-code" id="cb19"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb19-1"><a href="#cb19-1" aria-hidden="true" tabindex="-1"></a>orange <span class="ot"><-</span> nc <span class="sc">|></span> dplyr<span class="sc">::</span><span class="fu">filter</span>(NAME <span class="sc">==</span> <span class="st">"Orange"</span>)</span>
<span id="cb19-2"><a href="#cb19-2" aria-hidden="true" tabindex="-1"></a>wd <span class="ot"><-</span> <span class="fu">st_is_within_distance</span>(nc, orange, </span>
<span id="cb19-3"><a href="#cb19-3" aria-hidden="true" tabindex="-1"></a> units<span class="sc">::</span><span class="fu">set_units</span>(<span class="dv">50</span>, km))</span>
<span id="cb19-4"><a href="#cb19-4" aria-hidden="true" tabindex="-1"></a>o50 <span class="ot"><-</span> nc <span class="sc">|></span> dplyr<span class="sc">::</span><span class="fu">filter</span>(<span class="fu">lengths</span>(wd) <span class="sc">></span> <span class="dv">0</span>)</span>
<span id="cb19-5"><a href="#cb19-5" aria-hidden="true" tabindex="-1"></a><span class="fu">nrow</span>(o50)</span>
<span id="cb19-6"><a href="#cb19-6" aria-hidden="true" tabindex="-1"></a><span class="co"># [1] 17</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
</div>
<p>(where we use <code>dplyr::filter</code> rather than <code>filter</code> to avoid confusion with <code>filter</code> from base R.)</p>
<p><a href="#fig-orangebuffer">Figure <span>7.3</span></a> shows the results of this analysis, and in addition a buffer around the county borders. Note that this buffer serves for illustration: it was <em>not</em> used to select the counties.</p>
<div class="cell">
<details>
<summary>Code</summary>
<div class="sourceCode cell-code" id="cb20"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb20-1"><a href="#cb20-1" aria-hidden="true" tabindex="-1"></a>og <span class="ot"><-</span> <span class="fu">st_geometry</span>(orange)</span>
<span id="cb20-2"><a href="#cb20-2" aria-hidden="true" tabindex="-1"></a>buf50 <span class="ot"><-</span> <span class="fu">st_buffer</span>(og, units<span class="sc">::</span><span class="fu">set_units</span>(<span class="dv">50</span>, km))</span>
<span id="cb20-3"><a href="#cb20-3" aria-hidden="true" tabindex="-1"></a>all <span class="ot"><-</span> <span class="fu">c</span>(buf50, <span class="fu">st_geometry</span>(o50))</span>
<span id="cb20-4"><a href="#cb20-4" aria-hidden="true" tabindex="-1"></a><span class="fu">plot</span>(<span class="fu">st_geometry</span>(o50), <span class="at">lwd =</span> <span class="dv">2</span>, <span class="at">extent =</span> all)</span>
<span id="cb20-5"><a href="#cb20-5" aria-hidden="true" tabindex="-1"></a><span class="fu">plot</span>(og, <span class="at">col =</span> <span class="st">'orange'</span>, <span class="at">add =</span> <span class="cn">TRUE</span>)</span>
<span id="cb20-6"><a href="#cb20-6" aria-hidden="true" tabindex="-1"></a><span class="fu">plot</span>(buf50, <span class="at">add =</span> <span class="cn">TRUE</span>, <span class="at">col =</span> <span class="cn">NA</span>, <span class="at">border =</span> <span class="st">'brown'</span>)</span>
<span id="cb20-7"><a href="#cb20-7" aria-hidden="true" tabindex="-1"></a><span class="fu">plot</span>(<span class="fu">st_geometry</span>(nc), <span class="at">add =</span> <span class="cn">TRUE</span>, <span class="at">border =</span> <span class="st">'grey'</span>)</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
</details>
<div class="cell-output-display">
<div id="fig-orangebuffer" class="quarto-figure quarto-figure-center anchored">
<figure class="figure">
<p><img src="07-Introsf_files/figure-html/fig-orangebuffer-1.png" class="img-fluid figure-img" style="width:100.0%"></p>
<figcaption class="figure-caption">Figure 7.3: Orange County (orange), counties within a 50 km radius (black), a 50~km buffer around Orange County (brown), and remaining counties (grey)</figcaption>
</figure>
</div>
</div>
</div>
</section>
</section>
<section id="spatial-joins" class="level2" data-number="7.2">
<h2 data-number="7.2" class="anchored" data-anchor-id="spatial-joins"><span class="header-section-number">7.2</span> Spatial joins</h2>
<p> </p>
<p>In regular (left, right, or inner) joins, <em>joined</em> records from a pair of tables are reported when one or more selected attributes match (are identical) in both tables. A spatial join is similar, but the criterion to join records is not equality of attributes but a spatial predicate. This leaves a wide variety of options in order to define <em>spatially</em> matching records, using binary predicates listed in <a href="03-Geometries.html#sec-de9im"><span>Section 3.2.2</span></a>. The concepts of “left”, “right”, “inner”, or “full” joins remain identical to the non-spatial join as the options for handling records that have no spatial match.</p>
<p>When using spatial joins, each record may have several matched records, yielding a large result table. A way to reduce this complexity may be to select from the matching records the one with the largest overlap with the target geometry. An example of this is shown (visually) in <a href="#fig-largest">Figure <span>7.4</span></a>; this is done using <code>st_join</code> with argument <code>largest = TRUE</code>.</p>
<div class="cell">
<details>
<summary>Code</summary>
<div class="sourceCode cell-code" id="cb21"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb21-1"><a href="#cb21-1" aria-hidden="true" tabindex="-1"></a><span class="co"># example of largest = TRUE:</span></span>
<span id="cb21-2"><a href="#cb21-2" aria-hidden="true" tabindex="-1"></a><span class="fu">system.file</span>(<span class="st">"shape/nc.shp"</span>, <span class="at">package=</span><span class="st">"sf"</span>) <span class="sc">|></span> </span>
<span id="cb21-3"><a href="#cb21-3" aria-hidden="true" tabindex="-1"></a> <span class="fu">read_sf</span>() <span class="sc">|></span></span>
<span id="cb21-4"><a href="#cb21-4" aria-hidden="true" tabindex="-1"></a> <span class="fu">st_transform</span>(<span class="st">'EPSG:2264'</span>) <span class="ot">-></span> nc</span>
<span id="cb21-5"><a href="#cb21-5" aria-hidden="true" tabindex="-1"></a>gr <span class="ot"><-</span> <span class="fu">st_sf</span>(</span>
<span id="cb21-6"><a href="#cb21-6" aria-hidden="true" tabindex="-1"></a> <span class="at">label =</span> <span class="fu">apply</span>(<span class="fu">expand.grid</span>(<span class="dv">1</span><span class="sc">:</span><span class="dv">10</span>, LETTERS[<span class="dv">10</span><span class="sc">:</span><span class="dv">1</span>])[,<span class="dv">2</span><span class="sc">:</span><span class="dv">1</span>], <span class="dv">1</span>, paste0, <span class="at">collapse =</span> <span class="st">""</span>),</span>
<span id="cb21-7"><a href="#cb21-7" aria-hidden="true" tabindex="-1"></a> <span class="at">geom =</span> <span class="fu">st_make_grid</span>(nc))</span>
<span id="cb21-8"><a href="#cb21-8" aria-hidden="true" tabindex="-1"></a>gr<span class="sc">$</span>col <span class="ot"><-</span> <span class="fu">sf.colors</span>(<span class="dv">10</span>, <span class="at">categorical =</span> <span class="cn">TRUE</span>, <span class="at">alpha =</span> .<span class="dv">3</span>)</span>
<span id="cb21-9"><a href="#cb21-9" aria-hidden="true" tabindex="-1"></a><span class="co"># cut, to verify that NA's work out:</span></span>
<span id="cb21-10"><a href="#cb21-10" aria-hidden="true" tabindex="-1"></a>gr <span class="ot"><-</span> gr[<span class="sc">-</span>(<span class="dv">1</span><span class="sc">:</span><span class="dv">30</span>),]</span>
<span id="cb21-11"><a href="#cb21-11" aria-hidden="true" tabindex="-1"></a><span class="fu">suppressWarnings</span>(nc_j <span class="ot"><-</span> <span class="fu">st_join</span>(nc, gr, <span class="at">largest =</span> <span class="cn">TRUE</span>))</span>
<span id="cb21-12"><a href="#cb21-12" aria-hidden="true" tabindex="-1"></a><span class="fu">par</span>(<span class="at">mfrow =</span> <span class="fu">c</span>(<span class="dv">2</span>,<span class="dv">1</span>), <span class="at">mar =</span> <span class="fu">rep</span>(<span class="dv">0</span>,<span class="dv">4</span>))</span>
<span id="cb21-13"><a href="#cb21-13" aria-hidden="true" tabindex="-1"></a><span class="fu">plot</span>(<span class="fu">st_geometry</span>(nc_j), <span class="at">border =</span> <span class="st">'grey'</span>)</span>
<span id="cb21-14"><a href="#cb21-14" aria-hidden="true" tabindex="-1"></a><span class="fu">plot</span>(<span class="fu">st_geometry</span>(gr), <span class="at">add =</span> <span class="cn">TRUE</span>, <span class="at">col =</span> gr<span class="sc">$</span>col)</span>
<span id="cb21-15"><a href="#cb21-15" aria-hidden="true" tabindex="-1"></a><span class="fu">text</span>(<span class="fu">st_coordinates</span>(<span class="fu">st_centroid</span>(<span class="fu">st_geometry</span>(gr))), <span class="at">labels =</span> gr<span class="sc">$</span>label, <span class="at">cex =</span> .<span class="dv">85</span>)</span>
<span id="cb21-16"><a href="#cb21-16" aria-hidden="true" tabindex="-1"></a><span class="co"># the joined dataset:</span></span>
<span id="cb21-17"><a href="#cb21-17" aria-hidden="true" tabindex="-1"></a><span class="fu">plot</span>(<span class="fu">st_geometry</span>(nc_j), <span class="at">border =</span> <span class="st">'grey'</span>, <span class="at">col =</span> nc_j<span class="sc">$</span>col)</span>
<span id="cb21-18"><a href="#cb21-18" aria-hidden="true" tabindex="-1"></a><span class="fu">text</span>(<span class="fu">st_coordinates</span>(<span class="fu">st_centroid</span>(<span class="fu">st_geometry</span>(nc_j))), <span class="at">labels =</span> nc_j<span class="sc">$</span>label, <span class="at">cex =</span> .<span class="dv">7</span>)</span>
<span id="cb21-19"><a href="#cb21-19" aria-hidden="true" tabindex="-1"></a><span class="fu">plot</span>(<span class="fu">st_geometry</span>(gr), <span class="at">border =</span> <span class="st">'#88ff88aa'</span>, <span class="at">add =</span> <span class="cn">TRUE</span>)</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
</details>
<div class="cell-output-display">
<div id="fig-largest" class="quarto-figure quarto-figure-center anchored">
<figure class="figure">
<p><img src="07-Introsf_files/figure-html/fig-largest-1.png" class="img-fluid figure-img" style="width:100.0%"></p>
<figcaption class="figure-caption">Figure 7.4: Example of <code>st_join</code> with <code>largest = TRUE</code>: the label of the polygon in the top figure with the largest intersection with polygons in the bottom figure is assigned to the polygons of the bottom figure.</figcaption>
</figure>
</div>
</div>
</div>
<p> </p>
<p>Another way to reduce the result set is to use <code>aggregate</code> after a join, to merge all matching records, and union their geometries; see <a href="05-Attributes.html#sec-updownscaling"><span>Section 5.4</span></a>.</p>
<section id="sampling-gridding-interpolating" class="level3">
<h3 class="anchored" data-anchor-id="sampling-gridding-interpolating">Sampling, gridding, interpolating</h3>
<p>Several convenience functions are available in package <strong>sf</strong>, some of which will be discussed here. Function <code>st_sample</code> generates a sample of points randomly sampled from target geometries, where target geometries can be point, line, or polygon geometries. Sampling strategies can be (completely) random, regular, or (with polygons) triangular. <a href="11-PointPattern.html"><span>Chapter 11</span></a> explains how spatial sampling (or point pattern simulation) methods available in package <strong>spatstat</strong> are interfaced through <code>st_sample</code>.</p>
<p>Function <code>st_make_grid</code> creates a square, rectangular, or hexagonal grid over a region, or points with the grid centres or corners. It was used to create the rectangular grid in <a href="#fig-largest">Figure <span>7.4</span></a>.</p>
<p></p>
<p>Function <code>st_interpolate_aw</code> “interpolates” area values to new areas, as explained in <a href="05-Attributes.html#sec-area-weighted"><span>Section 5.3</span></a>, both for intensive and extensive variables.</p>
<p> </p>
</section>
</section>
<section id="sec-ccw" class="level2" data-number="7.3">
<h2 data-number="7.3" class="anchored" data-anchor-id="sec-ccw"><span class="header-section-number">7.3</span> Ellipsoidal coordinates</h2>
<p>Unprojected data have ellipsoidal coordinates, expressed in degrees east and north. As explained in <a href="04-Spherical.html#sec-straight"><span>Section 4.1</span></a>, “straight” lines between points are the curved shortest paths (“geodesic”). By default, <strong>sf</strong> uses geometrical operations from the <code>s2geometry</code> library, interfaced through the <strong>s2</strong> package <span class="citation" data-cites="R-s2">(<a href="references.html#ref-R-s2" role="doc-biblioref">Dunnington, Pebesma, and Rubak 2023</a>)</span>, and we see for instance that the point</p>
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<div class="sourceCode cell-code" id="cb22"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb22-1"><a href="#cb22-1" aria-hidden="true" tabindex="-1"></a><span class="st">"POINT(50 50.1)"</span> <span class="sc">|></span> <span class="fu">st_as_sfc</span>(<span class="at">crs =</span> <span class="st">"OGC:CRS84"</span>) <span class="ot">-></span> pt</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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<div class="sourceCode cell-code" id="cb23"><pre class="sourceCode python code-with-copy"><code class="sourceCode python"><span id="cb23-1"><a href="#cb23-1" aria-hidden="true" tabindex="-1"></a><span class="im">import</span> geopandas <span class="im">as</span> gpd</span>
<span id="cb23-2"><a href="#cb23-2" aria-hidden="true" tabindex="-1"></a><span class="im">from</span> shapely.geometry <span class="im">import</span> Point, Polygon</span>
<span id="cb23-3"><a href="#cb23-3" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb23-4"><a href="#cb23-4" aria-hidden="true" tabindex="-1"></a>pt <span class="op">=</span> gpd.GeoSeries([Point(<span class="dv">50</span>, <span class="fl">50.1</span>)])</span>
<span id="cb23-5"><a href="#cb23-5" aria-hidden="true" tabindex="-1"></a>pt <span class="op">=</span> pt.set_crs(<span class="st">"OGC:CRS84"</span>)</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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<p>falls <em>inside</em> the polygon:</p>
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<div class="sourceCode cell-code" id="cb24"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb24-1"><a href="#cb24-1" aria-hidden="true" tabindex="-1"></a><span class="st">"POLYGON((40 40, 60 40, 60 50, 40 50, 40 40))"</span> <span class="sc">|></span></span>
<span id="cb24-2"><a href="#cb24-2" aria-hidden="true" tabindex="-1"></a> <span class="fu">st_as_sfc</span>(<span class="at">crs =</span> <span class="st">"OGC:CRS84"</span>) <span class="ot">-></span> pol</span>
<span id="cb24-3"><a href="#cb24-3" aria-hidden="true" tabindex="-1"></a><span class="fu">st_intersects</span>(pt, pol)</span>
<span id="cb24-4"><a href="#cb24-4" aria-hidden="true" tabindex="-1"></a><span class="co"># Sparse geometry binary predicate list of length 1, where the</span></span>
<span id="cb24-5"><a href="#cb24-5" aria-hidden="true" tabindex="-1"></a><span class="co"># predicate was `intersects'</span></span>
<span id="cb24-6"><a href="#cb24-6" aria-hidden="true" tabindex="-1"></a><span class="co"># 1: 1</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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<div class="sourceCode cell-code" id="cb25"><pre class="sourceCode python code-with-copy"><code class="sourceCode python"><span id="cb25-1"><a href="#cb25-1" aria-hidden="true" tabindex="-1"></a><span class="im">import</span> geopandas <span class="im">as</span> gpd</span>
<span id="cb25-2"><a href="#cb25-2" aria-hidden="true" tabindex="-1"></a><span class="im">from</span> shapely.geometry <span class="im">import</span> Point, Polygon</span>
<span id="cb25-3"><a href="#cb25-3" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb25-4"><a href="#cb25-4" aria-hidden="true" tabindex="-1"></a>pol <span class="op">=</span> gpd.GeoSeries([Polygon([(<span class="dv">40</span>,<span class="dv">40</span>), (<span class="dv">60</span>,<span class="dv">40</span>), (<span class="dv">60</span>,<span class="dv">50</span>), (<span class="dv">40</span>,<span class="dv">50</span>), (<span class="dv">40</span>,<span class="dv">40</span>)])])</span>
<span id="cb25-5"><a href="#cb25-5" aria-hidden="true" tabindex="-1"></a>pol <span class="op">=</span> pol.set_crs(<span class="st">"OGC:CRS84"</span>)</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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<p>as illustrated by <a href="#fig-figs2">Figure <span>7.5</span></a> (left: straight lines on an orthographic projection centred at the plot area).</p>
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<summary>Code</summary>
<div class="sourceCode cell-code" id="cb26"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb26-1"><a href="#cb26-1" aria-hidden="true" tabindex="-1"></a><span class="fu">par</span>(<span class="at">mfrow =</span> <span class="fu">c</span>(<span class="dv">1</span>, <span class="dv">2</span>))</span>
<span id="cb26-2"><a href="#cb26-2" aria-hidden="true" tabindex="-1"></a><span class="fu">par</span>(<span class="at">mar =</span> <span class="fu">c</span>(<span class="fl">2.1</span>, <span class="fl">2.1</span>, <span class="fl">1.2</span>, .<span class="dv">5</span>))</span>
<span id="cb26-3"><a href="#cb26-3" aria-hidden="true" tabindex="-1"></a>ortho <span class="ot"><-</span> <span class="fu">st_crs</span>(<span class="st">"+proj=ortho +lon_0=50 +lat_0=45"</span>)</span>
<span id="cb26-4"><a href="#cb26-4" aria-hidden="true" tabindex="-1"></a>pol <span class="sc">|></span> <span class="fu">st_transform</span>(ortho) <span class="sc">|></span> <span class="fu">plot</span>(<span class="at">axes =</span> <span class="cn">TRUE</span>, <span class="at">graticule =</span> <span class="cn">TRUE</span>, </span>
<span id="cb26-5"><a href="#cb26-5" aria-hidden="true" tabindex="-1"></a> <span class="at">main =</span> <span class="st">'s2geometry'</span>)</span>
<span id="cb26-6"><a href="#cb26-6" aria-hidden="true" tabindex="-1"></a>pt <span class="sc">|></span> <span class="fu">st_transform</span>(ortho) <span class="sc">|></span> <span class="fu">plot</span>(<span class="at">add =</span> <span class="cn">TRUE</span>, <span class="at">pch =</span> <span class="dv">16</span>, <span class="at">col =</span> <span class="st">'red'</span>)</span>
<span id="cb26-7"><a href="#cb26-7" aria-hidden="true" tabindex="-1"></a><span class="co"># second plot:</span></span>
<span id="cb26-8"><a href="#cb26-8" aria-hidden="true" tabindex="-1"></a><span class="fu">plot</span>(pol, <span class="at">axes =</span> <span class="cn">TRUE</span>, <span class="at">graticule =</span> <span class="cn">TRUE</span>, <span class="at">main =</span> <span class="st">'GEOS'</span>)</span>
<span id="cb26-9"><a href="#cb26-9" aria-hidden="true" tabindex="-1"></a><span class="fu">plot</span>(pt, <span class="at">add =</span> <span class="cn">TRUE</span>, <span class="at">pch =</span> <span class="dv">16</span>, <span class="at">col =</span> <span class="st">'red'</span>)</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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<div id="fig-figs2" class="quarto-figure quarto-figure-center anchored">
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<p><img src="07-Introsf_files/figure-html/fig-figs2-1.png" class="img-fluid figure-img" style="width:100.0%"></p>
<figcaption class="figure-caption">Figure 7.5: Intersection depends on whether we use geodesics/great circle arcs (left: s2) or Cartesian coordinates (right)</figcaption>
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<div class="sourceCode cell-code" id="cb27"><pre class="sourceCode python code-with-copy"><code class="sourceCode python"><span id="cb27-1"><a href="#cb27-1" aria-hidden="true" tabindex="-1"></a><span class="im">import</span> geopandas <span class="im">as</span> gpd</span>
<span id="cb27-2"><a href="#cb27-2" aria-hidden="true" tabindex="-1"></a><span class="im">import</span> matplotlib.pyplot <span class="im">as</span> plt</span>
<span id="cb27-3"><a href="#cb27-3" aria-hidden="true" tabindex="-1"></a><span class="im">from</span> descartes <span class="im">import</span> PolygonPatch</span>
<span id="cb27-4"><a href="#cb27-4" aria-hidden="true" tabindex="-1"></a><span class="im">from</span> shapely.geometry <span class="im">import</span> Point, Polygon</span>
<span id="cb27-5"><a href="#cb27-5" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb27-6"><a href="#cb27-6" aria-hidden="true" tabindex="-1"></a>point <span class="op">=</span> Point(<span class="dv">50</span>, <span class="fl">50.1</span>)</span>
<span id="cb27-7"><a href="#cb27-7" aria-hidden="true" tabindex="-1"></a>polygon <span class="op">=</span> Polygon([(<span class="dv">40</span>, <span class="dv">40</span>), (<span class="dv">60</span>, <span class="dv">40</span>), (<span class="dv">60</span>, <span class="dv">50</span>), (<span class="dv">40</span>, <span class="dv">50</span>), (<span class="dv">40</span>, <span class="dv">40</span>)])</span>
<span id="cb27-8"><a href="#cb27-8" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb27-9"><a href="#cb27-9" aria-hidden="true" tabindex="-1"></a>gdf_point <span class="op">=</span> gpd.GeoDataFrame(geometry<span class="op">=</span>[point])</span>
<span id="cb27-10"><a href="#cb27-10" aria-hidden="true" tabindex="-1"></a>gdf_poly <span class="op">=</span> gpd.GeoDataFrame(geometry<span class="op">=</span>[polygon])</span>
<span id="cb27-11"><a href="#cb27-11" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb27-12"><a href="#cb27-12" aria-hidden="true" tabindex="-1"></a><span class="bu">print</span>(gdf_point.intersects(gdf_poly))</span>
<span id="cb27-13"><a href="#cb27-13" aria-hidden="true" tabindex="-1"></a><span class="co"># 0 False</span></span>
<span id="cb27-14"><a href="#cb27-14" aria-hidden="true" tabindex="-1"></a><span class="co"># dtype: bool</span></span>
<span id="cb27-15"><a href="#cb27-15" aria-hidden="true" tabindex="-1"></a>ortho <span class="op">=</span> <span class="st">"+proj=ortho +lon_0=50 +lat_0=45"</span></span>
<span id="cb27-16"><a href="#cb27-16" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb27-17"><a href="#cb27-17" aria-hidden="true" tabindex="-1"></a>fig, axs <span class="op">=</span> plt.subplots(<span class="dv">1</span>, <span class="dv">2</span>, figsize<span class="op">=</span>(<span class="dv">10</span>, <span class="dv">5</span>))</span>
<span id="cb27-18"><a href="#cb27-18" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb27-19"><a href="#cb27-19" aria-hidden="true" tabindex="-1"></a>gdf_poly.set_crs(ortho).plot(ax<span class="op">=</span>axs[<span class="dv">0</span>], color<span class="op">=</span><span class="st">'none'</span>, edgecolor<span class="op">=</span><span class="st">'black'</span>)</span>
<span id="cb27-20"><a href="#cb27-20" aria-hidden="true" tabindex="-1"></a>gdf_point.set_crs(ortho).plot(ax<span class="op">=</span>axs[<span class="dv">0</span>], color<span class="op">=</span><span class="st">'red'</span>, marker<span class="op">=</span><span class="st">'o'</span>)</span>
<span id="cb27-21"><a href="#cb27-21" aria-hidden="true" tabindex="-1"></a>axs[<span class="dv">0</span>].set_xlim(<span class="dv">39</span>, <span class="dv">61</span>)</span>
<span id="cb27-22"><a href="#cb27-22" aria-hidden="true" tabindex="-1"></a><span class="co"># (39.0, 61.0)</span></span>
<span id="cb27-23"><a href="#cb27-23" aria-hidden="true" tabindex="-1"></a>axs[<span class="dv">0</span>].set_ylim(<span class="dv">33</span>, <span class="dv">56</span>)</span>
<span id="cb27-24"><a href="#cb27-24" aria-hidden="true" tabindex="-1"></a><span class="co"># (33.0, 56.0)</span></span>
<span id="cb27-25"><a href="#cb27-25" aria-hidden="true" tabindex="-1"></a>axs[<span class="dv">0</span>].grid(<span class="va">True</span>)</span>
<span id="cb27-26"><a href="#cb27-26" aria-hidden="true" tabindex="-1"></a>axs[<span class="dv">0</span>].set_title(<span class="st">'s2geometry'</span>)</span>
<span id="cb27-27"><a href="#cb27-27" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb27-28"><a href="#cb27-28" aria-hidden="true" tabindex="-1"></a>gdf_poly.set_crs(<span class="st">"OGC:CRS84"</span>).plot(ax<span class="op">=</span>axs[<span class="dv">1</span>], color<span class="op">=</span><span class="st">'none'</span>, edgecolor<span class="op">=</span><span class="st">'black'</span>)</span>
<span id="cb27-29"><a href="#cb27-29" aria-hidden="true" tabindex="-1"></a>gdf_point.set_crs(<span class="st">"OGC:CRS84"</span>).plot(ax<span class="op">=</span>axs[<span class="dv">1</span>], color<span class="op">=</span><span class="st">'red'</span>, marker<span class="op">=</span><span class="st">'o'</span>)</span>
<span id="cb27-30"><a href="#cb27-30" aria-hidden="true" tabindex="-1"></a>axs[<span class="dv">1</span>].set_xlim(<span class="dv">39</span>, <span class="dv">61</span>)</span>
<span id="cb27-31"><a href="#cb27-31" aria-hidden="true" tabindex="-1"></a><span class="co"># (39.0, 61.0)</span></span>
<span id="cb27-32"><a href="#cb27-32" aria-hidden="true" tabindex="-1"></a>axs[<span class="dv">1</span>].set_ylim(<span class="dv">34</span>, <span class="dv">56</span>)</span>
<span id="cb27-33"><a href="#cb27-33" aria-hidden="true" tabindex="-1"></a><span class="co"># (34.0, 56.0)</span></span>
<span id="cb27-34"><a href="#cb27-34" aria-hidden="true" tabindex="-1"></a>axs[<span class="dv">1</span>].set_title(<span class="st">'GEOS'</span>)</span>
<span id="cb27-35"><a href="#cb27-35" aria-hidden="true" tabindex="-1"></a>axs[<span class="dv">1</span>].grid(<span class="va">True</span>)</span>
<span id="cb27-36"><a href="#cb27-36" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb27-37"><a href="#cb27-37" aria-hidden="true" tabindex="-1"></a>plt.show()</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
</details>
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<div class="quarto-figure quarto-figure-center">
<figure class="figure">
<p><img src="07-Introsf_files/figure-html/unnamed-chunk-22-1.png" class="img-fluid figure-img" style="width:100.0%"></p>
<figcaption class="figure-caption">Intersection depends on whether we use geodesics/great circle arcs (left: s2) or Cartesian coordinates (right)</figcaption>
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<p>If one wants <strong>sf</strong> to use ellipsoidal coordinates as if they are Cartesian coordinates, the use of <strong>s2</strong> can be switched off:</p>
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<div class="sourceCode cell-code" id="cb28"><pre class="sourceCode r code-with-copy"><code class="sourceCode r"><span id="cb28-1"><a href="#cb28-1" aria-hidden="true" tabindex="-1"></a>old <span class="ot"><-</span> <span class="fu">sf_use_s2</span>(<span class="cn">FALSE</span>)</span>
<span id="cb28-2"><a href="#cb28-2" aria-hidden="true" tabindex="-1"></a><span class="co"># Spherical geometry (s2) switched off</span></span>
<span id="cb28-3"><a href="#cb28-3" aria-hidden="true" tabindex="-1"></a><span class="fu">st_intersects</span>(pol, pt)</span>
<span id="cb28-4"><a href="#cb28-4" aria-hidden="true" tabindex="-1"></a><span class="co"># although coordinates are longitude/latitude, st_intersects assumes</span></span>
<span id="cb28-5"><a href="#cb28-5" aria-hidden="true" tabindex="-1"></a><span class="co"># that they are planar</span></span>
<span id="cb28-6"><a href="#cb28-6" aria-hidden="true" tabindex="-1"></a><span class="co"># Sparse geometry binary predicate list of length 1, where the</span></span>
<span id="cb28-7"><a href="#cb28-7" aria-hidden="true" tabindex="-1"></a><span class="co"># predicate was `intersects'</span></span>
<span id="cb28-8"><a href="#cb28-8" aria-hidden="true" tabindex="-1"></a><span class="co"># 1: (empty)</span></span>
<span id="cb28-9"><a href="#cb28-9" aria-hidden="true" tabindex="-1"></a><span class="fu">sf_use_s2</span>(old) <span class="co"># restore</span></span>
<span id="cb28-10"><a href="#cb28-10" aria-hidden="true" tabindex="-1"></a><span class="co"># Spherical geometry (s2) switched on</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
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<p>and the intersection is empty, as illustrated by <a href="#fig-figs2">Figure <span>7.5</span></a> (right: straight lines on an equidistant cylindrical projection). The warning indicates the planar assumption for ellipsoidal coordinates.</p>
<p>Use of <strong>s2</strong> can be switched off for reasons of performance or compatibility with legacy implementations. The underlying libraries, <strong>GEOS</strong> for Cartesian and <strong>s2geometry</strong> for spherical geometry (<a href="01-hello.html#fig-gdal-fig-nodetails">Figure <span>1.7</span></a>) were developed with different motivations, and their use through <strong>sf</strong> differs in some respects:</p>
<ul>
<li>certain operations may be much faster in one compared to the other,</li>
<li>certain functions may be available in only one of them (like <code>st_relate</code> being only present in GEOS),</li>
<li>when using transformers, <strong>GEOS</strong> returns exterior polygon rings noded clockwise (<code>st_sfc(..., check_ring_dir = TRUE)</code> can be used to revert to counter-clockwise), <strong>s2geometry</strong> retuns them counter-clockwise</li>
</ul>