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<!DOCTYPE html>
<html lang="en">
<head>
<meta content="text/html; charset=utf-8" http-equiv="content-type" />
<title>Spatial Data on the Web Best Practices</title>
<!--
<script src="https://www.w3.org/Tools/respec/respec-w3c-common" class="remove" defer></script>
-->
<script src="https://www.w3.org/Tools/respec/respec-w3c" class="remove" defer></script>
<script class="remove" src="bpconfig.js"></script>
<script>
/* *********************************************************************************
@andrea-perego: replaced the following function with new ones, not using jQuery,
which is no longer supported in new versions of ReSpec. The new script is only in
charge of cross-referencing best practices, as cross-refering of examples is now
natively supported in ReSpec. In case ReSpec will eventually natively support
cross-referencing of best practices, this SCRIPT tag should be deleted, along
with the SCRIPT tag at the end of the current document, in charge of invoking it.
********************************************************************************* */
/* **
function popCrossRefs() {
$('a[href^="#"]').each( function () {
var href = $(this).attr('href');
var id = href.trim().replace('#','');
var text = $(this).text();
if (text.trim().length == 0 && id.length > 0 && ( $(href).hasClass('example') || $(href).hasClass('practicelab') )) {
var label = $('.example:has(#' + id + ') > .example-title, *[id="' + id + '"].example > .example-title, *[id="' + id + '"].illegal-example > .example-title).text();
if (label.trim().length > 0) {
$(this).text(label);
}
var label = $(*[id="' + id + '"].practicelab').text();
if (label.trim().length > 0) {
$(this).text(label);
}
}
} );
}
$(document).ready( function() {
popCrossRefs();
});
** */
var bp = new Array();
function getBPs() {
var el = document.getElementsByClassName("practice");
for(var i=0; i<el.length; i++) {
var nr = i+1;
var id = el[i].getElementsByClassName("practicelab")[0].id;
var title = el[i].getElementsByClassName("practicelab")[0].textContent.replace(/\s+/g, ' ');
var description = el[i].getElementsByClassName("practicedesc")[0].textContent.replace(/\s+/g, ' ');
var label = "Best Practice " + nr;
bp.push({"id": id, "nr": nr, "label": label, "title": title, "heading": label + ": " + title, "description": description});
}
}
function bpCrossRefs() {
var id;
var base_url = window.location.href.substring(0, window.location.href.length - ((window.location.search + window.location.hash).length));
var links = document.getElementsByTagName("a");
// var target = document.getElementsByClassName("practicelab");
getBPs();
for(var i=0; i<links.length; i++) {
if (links[i].href.startsWith(base_url + "#")) {
id = links[i].href.substring(base_url.length + 1);
// for(var j=0; j<target.length; j++) {
for(var j=0; j<bp.length; j++) {
// var bpn = j+1;
// if (target[j].id == id) {
if (bp[j].id == id && links[i].textContent.trim() == "") {
links[i].textContent = bp[j].heading;
}
}
}
}
}
// @andrea-perego
</script>
<script class="remove" src="benefits.js"></script>
<style type="text/css">
/* **
@andrea-perego: Part of the CSS statements have been commented as they were conflicting,
sometimes causing the non-intended effect, with ReSpec, which, after the publication of
the SDWBP NOTE, included specific styling for the some elements and classes used in the
SDWBP (including BPs, figures, tables).
All these comments include a double star (**) in the start and end comment delimiters.
Comments without ** were already present in the original ED.
** */
/* ** Statements added to fix some BP formatting issues ** */
.practicecontainer {
border: solid 1px #dddddd;
padding: 0 2em 0 2em;
margin-top:1em;
background-color:#fbfbfb;
}
.practicecontainer > .practice {margin:0 -2em;}
/* Force W3C logo to site side by side with OGC logo */
/* **
.head img[src*="logos/W3C"] {
display: inherit !important;
}
.head a:hover > img[src*='ogc'] {
opacity: 0.8;
}
** */
/* **
#bp-summary ul{
list-style-type: none;
padding-left: 0;
line-height: 1.6em;
background-color: #FCFAEE;
}
** */
.hidden {display:none}
ul.benefitsList li.icon {
display:inline;
list-style-type: none;
}
ul.benefitsList li.icon img {
padding:0;
margin-right:1em;
max-width:60px;
max-height: 70px;
}
ul.benefitsList li.icon img.comprehensionIcon, ul.benefitsList li.icon img.discoverabilityIcon, ul.benefitsList li.icon img.interoperabilityIcon, ul.benefitsList li.icon img.processabilityIcon {
max-width:80px;
}
ul.benefitsList li.icon img.discoverabilityIcon, ul.benefitsList li.icon img.interoperabilityIcon, ul.benefitsList li.icon img.processabilityIcon {
max-width:73px;
}
/* *************************************************************
These styles are for the lists of benefits
************************************************************** */
#benefitsTables {
width: 100%;
margin: 0 auto;
}
.benefit-list-panel {
border-radius: 1em;
padding: 0.2em 1em;
}
.benefit-list-panel ul {
list-style-type:none;
padding-left:0;
}
.benefit-list-panel ul li {
font-size:smaller;
line-height:1.4em;
}
.benefit-list-panel p.benefitsPanelTitle {
font-weight: bold;
text-transform: uppercase;
text-align: center;
}
#benefitListReuse {
background: #B0CC9B;
border: 1px solid #387F05;
}
#benefitListAccess {
background: #E8F1FA;
border: 1px solid #81B3E0;
}
#benefitListTrust {
background: #E6BE9F;
border: 1px solid #BF5B0E;
}
#benefitListDiscoverability {
background: #CCBEB5;
border: 1px solid #7F5C46;
}
#benefitListProcessability {
background: #C5B5DE;
border: 1px solid #6E46AD;
}
#benefitListInteroperability {
background: #F3E09A;
border: 1px solid #E0B200;
}
#benefitListLinkability {
background: #B9C1CC;
border: 1px solid #50637F;
}
#benefitListComprehension {
background: #B3B3B3;
border: 1px solid #404040;
}
/* *******************************************
We reuse the 2 column style (for screens > 600 wide) from the list of BPs
to create the columns for the lists of benefits
********************************************** */
@media screen and (min-width: 600px) {
/* ** #bp-summary ul, ** */ #benefitsTables {
column-count:2;
column-gap: 1em;
}
/* We need to re-set the column number to 1 so that within each panel there is only 1 column */
#benefitsTables .benefit-list-panel {
column-count:1;
margin:.1em;
display:inline-block; /* This prevents single lists spanning multiple columns, thank you http://stackoverflow.com/questions/6682501/css3-columns-widows-orphans */
width:90%; /* For somr reason some of the panels are wider than others, this stops that heppening */
}
}
/* And we can go to three columns for bigger screens */
@media screen and (min-width: 850px) {
#benefitsTables {
column-count:3;
column-gap: 1em;
}
}
/* Styles for the BPs themsevles */
/* **
.practice,
#tempPractice{
padding-left: 1em;
background-color: #FCFAEE;
border: thin solid black;
}
#tempPractice .tempPracticelab{
background-color: #dfffff;
position: relative;
top: -1.5em;
font-weight: bold;
}
.practice p.practicedesc,
#tempPractice p.tempPracticedesc{
font-style: italic;
border-bottom: thin solid black;
position: relative;
top: -1.5em;
margin: 0 2em -1em 1em;
;
}
.subhead{
font-weight: bold;
}
** */
.benefits .stamp {
height: 52px;
width: 52px;
margin-right: 4px;
margin-bottom: 4px;
}
.benefits .stamp-template {
height: 82px;
width: 82px;
margin-right: 4px;
margin-bottom: 4px;
}
/* **
.practice dl dt #tempPractice dl dt{
font-weight: normal;
}
** */
/* *******************************************
Figures
********************************************** */
/* **
figure{
text-align: center;
}
figure#contextDiagram{
width: 60%;
margin: 0 auto;
}
figure figcaption{
text-align: center;
font-style: italic;
}
** */
/* *******************************************
Tables
********************************************** */
/* **
table#ns-rdf-table,
table#ns-xml-table,
table.bptable {
border-collapse: collapse;
caption-side:bottom;
}
table#ns-rdf-table th, table#ns-rdf-table td,
table#ns-xml-table th, table#ns-xml-table td,
table.bptable th, table.bptable td {
border: 1px solid black;
padding:0.3em;
}
table#ns-rdf-table caption,
table#ns-xml-table caption,
table.bptable caption {
margin:0.5em;
font-style:italic;
}
table#relative-positioning-modes-table,
table.bptable {
border-collapse: collapse;
caption-side:bottom;
}
table#relative-positioning-modes-table th, table#relative-positioning-modes-table td, table.bptable th, table.bptable td {
border: 1px solid black;
padding:0.3em;
}
table#relative-positioning-modes-table caption,
table.bptable caption {
margin:0.5em;
font-style:italic;
}
table.bptable {
border-collapse: collapse;
caption-side:bottom;
}
** */
table#table-formats-matrix,
table#table-vocabs-matrix
{
font-size: .8em;
}
/*
table#x-ref_formatVbp,
table#detailed-format-matrix,
*/
/* **
table#table-formats-matrix,
table#table-vocabs-matrix
{
border-collapse: collapse;
caption-side: bottom;
}
table.bptable th,
table.bptable td,
** */
/*
table#x-ref_formatVbp th,
table#x-ref_formatVbp td,
table#detailed-format-matrix th,
table#detailed-format-matrix td,
*/
/* **
table#table-formats-matrix th,
table#table-formats-matrix td,
table#table-vocabs-matrix th,
table#table-vocabs-matrix td
{
border: 1px solid black;
padding: 0.3em;
}
table.bptable,
** */
/*
table#x-ref_formatVbp caption,
table#detailed-format-matrix caption,
*/
/* **
table#table-formats-matrix caption,
table#table-vocabs-matrix caption
{
margin: 0.5em;
font-style: italic;
}
** */
.stmt
{
padding: 3pt}
.stmt1
{
column-count: 2;
column-gap: 1em;
background-color: #FCFAEE;
}
.expand{
display: block;
cursor: pointer;
}
.expand:hover{
color: #3D3D3D;
}
.expand:before{
font-weight: bold;
content: "\25C6 Example (click to expand or collapse)";
}
.expand + input{
display: none;
}
.expand + input + *{
display: none;
}
.expand + input:checked + *{
display: block;
}
.benefits-items {
width: 100%;
margin: 0 auto;
}
.benefits-items .item {
border-radius: 22px;
width: 28%;
padding: 20px;
margin: 2px;
font-size: 13px;
line-height: 150%;
float: left;
}
.benefits-items .item .title {
font-size: 16px;
font-weight: 800;
text-transform: uppercase;
text-align: center;
}
.benefits-items .reuse {
background: #B0CC9B;
border: 1px solid #387F05;
}
.benefits-items .access {
background: #E8F1FA;
border: 1px solid #81B3E0;
}
.benefits-items .trust {
background: #E6BE9F;
border: 1px solid #BF5B0E;
float: right;
}
.benefits-items .discoverability {
background: #CCBEB5;
border: 1px solid #7F5C46;
}
.benefits-items .processability {
background: #C5B5DE;
border: 1px solid #6E46AD;
}
.benefits-items .interoperability {
background: #F3E09A;
border: 1px solid #E0B200;
float: right;
}
.benefits-items .linkability {
background: #B9C1CC;
border: 1px solid #50637F;
}
.benefits-items .comprehension {
background: #B3B3B3;
border: 1px solid #404040;
float: right;
}
@media screen and (min-width: 1024px) {
.benefits-items .item {
margin-left: 1.6%;
}
}
@media screen and (max-width: 900px) {
.benefits-items .item {
clear: both;
display: inline-block;
float: left !important;
width: 90%;
}
}
</style>
</head>
<body>
<p class="copyright"><a href="https://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 2020 <a href="http://www.opengeospatial.org/">OGC</a> & <a href="https://www.w3.org/"> <abbr title="World Wide Web Consortium">W3C</abbr> </a><sup>®</sup> (<a href="https://www.csail.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>, <a href="https://www.ercim.eu/"><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>, <a href="https://www.keio.ac.jp/">Keio</a>, <a href="https://ev.buaa.edu.cn/">Beihang</a>), <abbr title="World Wide Web Consortium">W3C</abbr> <a href="https://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>, <a href="https://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>, <a href="https://www.w3.org/Consortium/Legal/copyright-documents">W3C</a> and <a href="https://www.ogc.org/ogc/document">OGC</a> document use rules apply.</p>
<section id="abstract">
<p>This document advises on best practices related to the publication of spatial
data on the Web; the use of Web technologies <em>as they may be applied to location</em>.
The best practices presented here are intended for practitioners, including Web developers and geospatial
experts, and are compiled based on evidence of real-world application. These best practices
suggest a significant change of emphasis from traditional <a>Spatial Data Infrastructures</a> by
adopting an approach based on general Web standards. As location is often the common factor across multiple
datasets, <a>spatial data</a> is an especially useful addition to the Web of data.</p>
</section>
<section id="sotd">
<aside class="ednote">
<p>To be updated.</p>
</aside>
<p>This document is considered to be complete and is expected to be the final release by the <a href="https://www.w3.org/2015/spatial/">Spatial Data on the Web Working Group</a>. The editors would like to thank everyone for their feedback. Comments received during final review triggered a couple of updates since the previous release on 11 May 2017 (see <a href="#changes" class="sectionRef"></a> for details). This document is published as a <abbr title="World Wide Web Consortium">W3C</abbr> Working Group Note and as an <a href="http://www.opengeospatial.org/docs/bp"><abbr title="Open Geospatial Consortium">OGC</abbr> Best Practice</a> in accordance with <a href="https://www.w3.org/2017/Process-20170301/#Note" class="sectionRef"><abbr title="World Wide Web Consortium">W3C</abbr> Policy section 6.8 Publishing a Working Group or Interest Group Note</a> and <a href="http://docs.opengeospatial.org/pol/05-020r24/05-020r24.html#83" class="sectionRef"><abbr title="Open Geospatial Consortium">OGC</abbr> Policies and Procedures section 8.6 Best Practices Documents</a>.</p>
<p><strong>For <abbr title="Open Geospatial Consortium">OGC</abbr>:</strong> This document defines an <a href="http://www.opengeospatial.org/docs/bp"><abbr title="Open Geospatial Consortium">OGC</abbr> Best Practice</a> on a particular technology or approach related to an OGC standard. This document is not an OGC Standard and may not be referred to as an OGC Standard. However, this document is an official position of the OGC membership on this particular technology topic. This document was prepared by the Spatial Data on the Web Working Group (<a href="http://www.opengeospatial.org/projects/groups/sdwwg">SDWWG</a>) — a joint W3C-OGC project (see <a href="https://www.w3.org/2015/spatial/charter">charter</a>) — following W3C conventions.</p>
</section>
<section id="issue-summary" class="introductory">
</section>
<section id="intro" class="informative">
<h2>Introduction</h2>
<p>Increasing numbers of Web applications provide a means of accessing data. From simple
visualizations to sophisticated interactive tools, there is a growing reliance on data. The
open data movement has led to many national, regional and local governments publishing
their data through portals. Scientific and cultural heritage data is increasingly published
on the Web for reuse by others. Crowd-sourced and social media data are abundant on the Web.
Sensors, connected devices and services from domains such as energy, transport,
manufacturing and healthcare are becoming commonly integrated using the Web as a common data
sharing platform.</p>
<p>The Data on the Web Best Practices [[DWBP]] provide a set of recommendations that are
applicable to the publication of <em>all</em> types of data on the Web. Those best practices
cover aspects including data formats, data access, data identifiers, metadata, licensing and
provenance.</p>
<p>Within this document, we are concerned with <a>spatial data</a>: data that describes <em>anything</em> with spatial <a>extent</a> (i.e. size, shape or position). <a>Spatial data</a> is also known as <em>location information</em>.</p>
<p>Similarly to the challenges identified in [[DWBP]] relating to publishing data on the Web,
and therefore not making use of the full potential of the Web as a data sharing platform,
there is a lack of consistency in how people publish <a>spatial data</a>.</p>
<p>It is not that there is a lack of <a>spatial data</a> on the Web; the maps, satellite and street
level images offered by search engines are familiar and there are many more examples of
spatial data being used in Web applications.</p>
<aside class="example" id="ex-sfpark" title="SFpark">
<p><a href="http://sfpark.org/">SFpark</a>
is a Web site where users can look at a map of San Francisco to see where parking is
available and at what price. Parking prices are incrementally raised or lowered in SFpark
pilot areas based on demand. In this application, static data on existing parking spaces is
combined with changing data about where people park the most, which is measured by parking
sensors.</p>
</aside>
<p>However, the data that has been published is difficult to find and often problematic to
access for non-specialist users. The key problems we are trying to solve in this document
are discoverability, accessibility and interoperability. Our overarching goal is to enable
<a>spatial data</a> to be integrated within the wider Web of data; providing standard patterns and
solutions that help solve these problems.</p>
<p>Following these guidelines should result in your data fitting more with the <a href="https://www.go-fair.org/fair-principles/">FAIR Principles</a>.</p>
</section>
<section id="audience" class="informative">
<h2>Audience</h2>
<p>Our goal in writing this best practice document is to support the practitioners who are
responsible for publishing their <a>spatial data</a> on the Web or developing tools to make it easy
for others to work with spatial data.</p>
<p>We expect readers to be familiar both with the fundamental concepts of the architecture of
the Web [[WEBARCH]] and the generalized best practices related to the publication and usage
of data on the Web [[DWBP]].</p>
<p>We aim to provide two primary pathways into these best practices:</p>
<ol>
<li>for those already familiar with publishing data on the Web who want to better exploit
the spatial aspects of their data; and</li>
<li>for those who publish <a>spatial data</a> through <a>Spatial Data Infrastructures</a> and want to
better integrate that data within the wider Web ecosystem.</li>
</ol>
<p>In each case, we aim to help them provide incremental value to their data through
application of these best practices.</p>
<p>This document provides a wide range of examples that illustrate how these best practices
may be applied using specific technologies. We do not expect readers to be familiar with all
the technologies used herein; rather that readers can identify with the activities being
undertaken in the various examples and, in doing so, find relevant technologies that they
are already aware of or discover technologies that are new to them.</p>
</section>
<section id="scope" class="informative">
<h2>Scope</h2>
<section id="scope-spatialdata">
<h3>Spatial data</h3>
<p>All the best practices described in [[DWBP]] are relevant to the publication of <a>spatial data</a>
on the Web. Some, such as [[DWBP]] <a href="https://www.w3.org/TR/dwbp/#DataLicense">Best Practice 4: Provide data license information</a>
need no further elaboration in the context of <a>spatial data</a>.
However, other best practices from [[DWBP]] are further refined in this document to provide
more specific guidance for <a>spatial data</a>.</p>
<p>The best practices described below are intended to meet requirements derived from the
scenarios in [[SDW-UCR]] that describe how <a>spatial data</a> is commonly published and used on
the Web. However, working with <a>spatial data</a> can rapidly become complex — especially
for critical decision making where mis-use of data can present risks. These best practices
are intended to make it easier to work with <a>spatial data</a> on the Web, but do not attempt
to cover all aspects of <a>spatial data</a> usage.</p>
<aside class="ednote">
<p>Should a reference to [[RESPONSIBLE-USE-SPATIAL]] be included here, or elsewhere in the document?</p>
</aside>
<p>In line with the <a href="https://www.w3.org/2015/spatial/charter#bp">charter</a>, this
document provides advice on:</p>
<ul>
<li>The choice of vocabulary and data format to be used when encoding <a>spatial data</a>;</li>
<li>The use of URIs for identifiers of resources described in spatial data;</li>
<li>The use of metadata to complement spatial data; and</li>
<li>The use of <abbr title="Application Programming Interfaces">APIs</abbr> to expose spatial data.</li>
</ul>
<p>As stated in the <a href="https://www.w3.org/2015/spatial/charter#bp">charter</a>, discussion of activities relating to rendering <a>spatial data</a> as maps is explicitly out of scope.</p>
<p>The original intent of these best practices was to cover aspects relating to all types of <a>spatial data</a>, for example: the arrangement of cells on a microscope slide; the position of things on the surface of the Earth, the Moon, Mars or other celestial bodies; the position of planets in the solar system etc. However, due to resource limitations these best practices deal almost exclusively with <a>geospatial data</a>; data about things that are implicitly or explicitly located relative to the Earth. That said, many of the best practices are applicable to wider <a>spatial data</a> concerns. In the remainder of the document, we simply refer to <a>spatial data</a> for brevity.</p>
<p>We extend [[DWBP]] to cover aspects specifically relating to <a>spatial data</a>,
introducing new best practices only where necessary. In particular, we consider the
individual resources, or <a>Spatial Things</a>, that are described within a dataset.</p>
</section>
<section id="scope-datapub">
<h3>Data publication</h3>
<p>In this document, we focus on the needs of data publishers and the developers that provide tools for them. That said, we recognize that value can only be gained from <em>publishing</em> the <a>spatial data</a> when people <em>use</em> it! Although we do not directly address the needs of those users, we ask that data publishers and developers reading this document do not forget about them; moreover, that they always consider the needs of users when publishing spatial data or developing the supporting tools. All our best practices are intended to provide guidance about publishing <a>spatial data</a> to improve ease of use.</p>
<p>Neither the wider topic of spatial data <em>management</em> nor <a>Spatial Data Infrastructures</a> are covered. We assume that your spatial data already exists and will be available from one of the following places:</p>
<ol>
<li>plain text documents; e.g. historical texts, government reports, blog posts etc.</li>
<li>data files containing structured content or markup; e.g. geospatial vector data in [[GeoPackage]] or [[GML]] format, statistical data in tabular <a>CSV</a> format or a spreadsheet, as <a href="https://it.wikipedia.org/wiki/GPS_eXchange_Format"><abbr title="GPS eXchange Format">GPX</abbr></a> data with “waypoints” and “tracks”, satellite imagery in <a href="https://en.wikipedia.org/wiki/GeoTIFF">GeoTIFF</a>, climate simulations in <a href="https://en.wikipedia.org/wiki/NetCDF#Conventions"><abbr title="netCDF Climate and Forecast Metadata Conventions">CF-NetCDF</abbr></a> etc.</li>
<li>a data repository; e.g. <a href="https://postgis.net/">PostGIS</a> (a spatially enabled relational database), <a href="https://en.wikipedia.org/wiki/Elasticsearch">Elasticsearch</a> (a document-oriented noSQL repository based on Apache Lucene), <a href="https://jena.apache.org/documentation/tdb/">Apache Jena’s TDB</a> (an RDF <a>triple store</a>)</li>
<li>exposed via an existing <abbr title="Application Programming Interface">API</abbr>; including OGC-compliant Web services and API's such as <a>WFS</a> [[WFS]], <a>WCS</a> [[WCS]] and <a>OGC API - Features</a> [[OAF1]].</li>
</ol>
<p>If your <a>spatial data</a> is managed within a software system it is likely that you will be able to access that data through one or more of the methods identified above; as structured data from a bulk extract (e.g. a “data dump”), via direct access to the underpinning data repository or through a bespoke or standards-compliant API provided by the system.</p>
<p>Each of the four starting points outlined above have their own challenges, but working with plain text documents can be particularly tricky as you will need to parse the natural language to identify the <a>Spatial Things</a> and their properties before you can proceed any further. Natural Language Processing (NLP) is a complex topic in its own right and is beyond the scope of this best practice document. We will assume that you’ve already completed this step and have parsed any plain documents into structured data records of some kind.</p>
</section>
<section id="scope-FAIR">
<h3>FAIR Principles</h3>
<p>The FAIR Principles are described at <a href="https://www.go-fair.org/fair-principles/">FAIR Principles - GO FAIR</a>; they are widely adopted (or at least aimed for)
when publishing scientific data including environmental and earth observation data.
Although the FAIR principles concentrate on machine readable data, whilst these best practices also cover “data for humans”,
there is a lot of overlap between the FAIR Principles and the best practices described in this paper.</p>
<p>Similarly, although not currently expressed in terms of the FAIR Principles,
the Data on the Web Best Practices are also designed to make it easier for "data consumers to find, use and link to the data".</p>
<p>The OGC is developing a new generation of resource-oriented HTTP APIs (e.g. <a>OGC API - Features</a> [[OAF1]]) for spatial data that align closely with FAIR principles.</p>
<p>There have also been some suggestions for improvement on the FAIR principles, and these are also discussed <a href="#FAIRPrinciples" class="sectionRef"></a>.</p>
</section>
<section id="best-practice-criteria">
<h3>Best practice criteria</h3>
<p>The best practices described in this document are compiled based on evidence of real-world
application in production environments. By ‘production environment’ we mean a case where <a>spatial data</a> has been delivered on the Web with the intention of being used by end users and with a quality level expected from such data. Where the <a href="http://www.opengeospatial.org/projects/groups/sdwwg">Working
Group</a> has identified issues that inhibit the use or interoperability of spatial data
on the Web, yet no evidence of real-world application is available, the editors present
these issues to the reader for consideration, along with any approaches recommended by the
Working Group. Please see <a href="#conclusions" class="sectionRef"></a> for further details. Such recommendations are clearly distinguished as such to ensure
that they are not confused with evidence-based best practice.</p>
<p>The normative element of each best practice is the <em>intended outcome</em>. Possible
implementations are suggested and, where appropriate, these recommend the use of a
particular technology.</p>
<p>We intend this best practice to be durable; that is that the best practices remain relevant
for many years to come as the specific technologies change. However, to provide
actionable guidance, i.e. to provide readers with the technical information they need to get
their <a>spatial data</a> on the Web, we try to balance between durable advice (that is necessarily
general) and examples using currently available technologies that illustrate how these best
practices can be implemented. We expect that readers will continue to be able to derive
insight from the examples even when those specifically mentioned technologies are no longer
in common usage, understanding that technology ‘y’ has replaced technology ‘x’.</p></section>
<section id="scope-privacy">
<h3>Privacy considerations</h3>
<p>There are many situations where the location of a person is very useful; from using a taxi hailing service to <a>geocoding</a> a selfie. Technology makes this location information easy to collect and share. However, <a>spatial data</a> has particular characteristics which makes its use potentially more complex. For example, a single location of an anonymous tracked mobile phone may cause few privacy concerns, however the same phone tracked over a few days could provide enough information to make the identification of its user possible. Like all personally identifiable information, great care must be taken as the collection, management and security of such information is the subject of legal frameworks. We do not attempt to provide guidance as to legal aspects of storing potentially personally identifiable spatial information; expert legal advice should be obtained. In summary: legal and privacy considerations relating to spatial data are out of scope.</p>
<aside class="ednote">
<p>Should a reference to [[RESPONSIBLE-USE-SPATIAL]] be included here, or elsewhere in the document?</p>
</aside>
</section>
</section>
<section id="bp-summary">
<h2>Best Practices Summary</h2>
<p>This document contains a variety of best practices related to the publication and usage of <a>spatial data</a> on the Web. First, it continues with several more in-depth introductions on <a>Spatial Things</a> and <a>geometry</a>, <a>coverages</a>, <a>spatial relations</a>, <a>coordinate reference systems</a>, <a>linked data</a>, and <a>Spatial Data Infrastructures</a>. After that, the best practices themselves are described. </p>
<p>The following best practices can be found in this document:</p>
<aside class="ednote">
<p>The duplication of the section heading is a ReSpec bug - see <a href="https://github.com/w3c/respec/issues/3278">w3c/respec/issues/3278</a>.</p>
</aside>
</section>
<section id="namespaces" class="informative">
<h2> Namespaces </h2>
<section id="ns-intro">
<h3> General remarks </h3>
<p>This document uses a unique abbreviation ("prefix") for each RDF namespace and XML namespace listed in this section. The namespace IRI can always be determined from the declaration of the namespace abbreviation.</p>
</section>
<section id="ns-rdf">
<h3> RDF Namespaces </h3>
<p>The following RDF namespace prefixes are used within this document. Use of a namespace does not imply endorsement of the associated data platform or vocabulary.</p>
<table class="simple" id="ns-rdf-table">
<caption>RDF namespaces used in the document</caption>
<thead>
<tr>
<th>Prefix</th>
<th>Namespace IRI</th>
<th>Source</th>
</tr>
</thead>
<tbody>
<tr>
<td><code>admingeo</code></td>
<td>http://data.ordnancesurvey.co.uk/ontology/admingeo/</td>
<td><a href="https://www.ordnancesurvey.co.uk/">Ordnance Survey's</a> <a href="http://data.ordnancesurvey.co.uk/ontology/admingeo/">Administrative geography and civil voting area ontology</a></td>
</tr>
<tr>
<td><code>adms</code></td>
<td>http://www.w3.org/ns/adms#</td>
<td>Asset Description Metadata Schema (ADMS) [[VOCAB-ADMS]]</td>
</tr>
<tr>
<td><code>bag</code></td>
<td>http://bag.basisregistraties.overheid.nl/def/bag#</td>
<td><a href="http://bag.basisregistraties.overheid.nl">Dutch Government Base Registry Adressen en Gebouwen (BAG)</a></td>
</tr>
<tr>
<td><code>dcat</code></td>
<td>http://www.w3.org/ns/dcat#</td>
<td>Data Catalog Vocabulary (DCAT) [[VOCAB-DCAT-2]]</td>
</tr>
<tr>
<td><code>dcterms</code></td>
<td>http://purl.org/dc/terms/</td>
<td>Dublin Core Metadata Initiative (DCMI) Metadata Terms [[DCTERMS]]</td>
</tr>
<tr>
<td><code>dqv</code></td>
<td>http://www.w3.org/ns/dqv#</td>
<td>DWBP Data Quality Vocabulary (DQV) [[VOCAB-DQV]]</td>
</tr>
<tr>
<td><code>foaf</code></td>
<td>http://xmlns.com/foaf/0.1/</td>
<td><a href="http://xmlns.com/foaf/spec/">FOAF Vocabulary Specification</a></td>
</tr>
<tr>
<td><code>geodcatap</code></td>
<td>http://data.europa.eu/930/</td>
<td>GeoDCAT-AP: A geospatial extension for the DCAT application profile for data portals in Europe [[GeoDCAT-AP]]</td>
</tr>
<tr>
<td><code>geom</code></td>
<td>http://data.ordnancesurvey.co.uk/ontology/geometry/</td>
<td><a href="https://www.ordnancesurvey.co.uk/">Ordnance Survey's</a> <a href="http://data.ordnancesurvey.co.uk/ontology/geometry/">Geometry Ontology</a></td>
</tr>
<tr>
<td><code>geonames</code></td>
<td>http://www.geonames.org/ontology#</td>
<td><a href="http://www.geonames.org/ontology/documentation.html">GeoNames Ontology</a></td>
</tr>
<tr>
<td><code>georss</code></td>
<td>http://www.georss.org/georss/</td>
<td>GeoRSS :: Geographically Encoded Objects for RSS feeds [[GeoRSS]], Geo OWL encoding</td>
</tr>
<tr>
<td><code>geosparql</code></td>
<td>http://www.opengis.net/ont/geosparql#</td>
<td>GeoSPARQL — A Geographic Query Language for RDF Data [[GeoSPARQL]]</td>
</tr>
<tr>
<td><code>gml-ont</code></td>
<td>http://www.opengis.net/ont/gml#</td>
<td>GeoSPARQL — A Geographic Query Language for RDF Data [[GeoSPARQL]]</td>
</tr>
<tr>
<td><code>ldqd</code></td>
<td>http://www.w3.org/2016/05/ldqd#</td>
<td>DWBP Data Quality Vocabulary (DQV) [[VOCAB-DQV]]: Data quality categories and dimensions</td>
</tr>
<tr>
<td><code>locn</code></td>
<td>http://www.w3.org/ns/locn#</td>
<td>ISA Location Core Vocabulary [[LOCN]]</td>
</tr>
<tr>
<td><code>osuk</code></td>
<td>http://data.ordnancesurvey.co.uk/id/</td>
<td><a href="http://data.ordnancesurvey.co.uk/">Ordnance Survey Linked Data Platform</a></td>
</tr>
<tr>
<td><code>ov</code></td>
<td>http://open.vocab.org/terms/</td>
<td><a href="http://vocab.org/open/">Open.vocab.org</a></td>
</tr>
<tr>
<td><code>owl</code></td>
<td>http://www.w3.org/2002/07/owl#</td>
<td>Web Ontology Language (OWL) [[OWL2-OVERVIEW]]</td>
</tr>
<tr>
<td><code>pdok</code></td>
<td>http://data.pdok.nl/def/pdok#</td>
<td><a href="https://data.pdok.nl/def/pdok">PDOK Data Platform</a></td>
</tr>
<tr>
<td><code>qudt</code></td>
<td>http://qudt.org/schema/qudt#</td>
<td><a href="http://qudt.org/">Quantities, Units, Dimensions and Data Types Ontologies (QUDT)</a></td>
</tr>
<tr>
<td><code>rdf</code></td>
<td>http://www.w3.org/1999/02/22-rdf-syntax-ns#</td>
<td>Resource Description Framework (RDF) [[RDF11-PRIMER]]</td>
</tr>
<tr>
<td><code>rdfs</code></td>
<td>http://www.w3.org/2000/01/rdf-schema#</td>
<td>RDF Schema vocabulary (RDFS) [[RDF-SCHEMA]]</td>
</tr>
<tr>
<td><code>schema</code></td>
<td>http://schema.org/</td>
<td>Schema.org [[SCHEMA-ORG]]</td>
</tr>
<tr>
<td><code>scotgov-stat</code></td>
<td>http://statistics.gov.scot/id/statistical-geography/</td>
<td><a href="http://statistics.gov.scot/">STATISTICS.GOV.SCOT</a> Geography Linked Data</td>
</tr>
<tr>
<td><code>sdmx-attribute</code></td>
<td>http://purl.org/linked-data/sdmx/2009/attribute#</td>
<td>The RDF Data Cube Vocabulary [[VOCAB-DATA-CUBE]]: Attribute properties</td>
</tr>
<tr>
<td><code>sf</code></td>
<td>http://www.opengis.net/ont/sf#</td>
<td>GeoSPARQL — A Geographic Query Language for RDF Data [[GeoSPARQL]]</td>
</tr>
<tr>
<td><code>skos</code></td>
<td>http://www.w3.org/2004/02/skos/core#</td>
<td>Simple Knowledge Organization System (SKOS) [[SKOS-PRIMER]]</td>
</tr>
<tr>
<td><code>ukgov-stat</code></td>
<td>http://statistics.data.gov.uk/id/statistical-geography/</td>
<td><a href="http://statistics.data.gov.uk/">Office for National Statistics</a> Geography Linked Data</td>
</tr>
<tr>
<td><code>vcard</code></td>
<td>http://www.w3.org/2006/vcard/ns#</td>
<td>vCard Ontology — for describing People and Organizations [[VCARD-RDF]]</td>
</tr>
<tr>
<td><code>void</code></td>
<td>http://rdfs.org/ns/void#</td>
<td>Describing Linked Datasets with the VoID Vocabulary [[VoID]]</td>
</tr>
<tr>
<td><code>w3cgeo</code></td>
<td>http://www.w3.org/2003/01/geo/wgs84_pos#</td>
<td>Basic Geo (WGS 84 lat/long) Vocabulary [[W3C-BASIC-GEO]]</td>
</tr>
</tbody>
</table>
</section>
<section id="ns-xml">
<h3> XML Namespaces </h3>
<p>The following XML namespace prefixes are used within this document. Use of a namespace does not imply endorsement of the associated XML schema.</p>
<table class="simple" id="ns-xml-table">
<caption>XML namespaces used in the document</caption>
<tbody>
<tr>
<th>Prefix</th>
<th>Namespace IRI</th>
<th>Source</th>
</tr>
<tr>
<td><code>bagwfs</code></td>
<td>http://bag.geonovum.nl</td>
<td><a href="http://geodata.nationaalgeoregister.nl/bag/wfs?service=WFS&version=2.0.0&request=DescribeFeatureType&typeName=bag%3Apand">XML schema</a> for the <a href="http://bag.basisregistraties.overheid.nl">Dutch Government Base Registry Adressen en Gebouwen (BAG)</a></td>
</tr>
<tr>
<td><code>gml</code></td>
<td>http://www.opengis.net/gml/3.2</td>
<td>Geography Markup Language (GML) Encoding Standard [[GML]]</td>
</tr>
<tr>
<td><code>sam</code></td>
<td>http://www.opengis.net/sampling/2.0</td>
<td>Observations and Measurements — XML Implementation [[OM-XML]]</td>
</tr>
<tr>
<td><code>sams</code></td>
<td>http://www.opengis.net/samplingSpatial/2.0</td>
<td>Observations and Measurements — XML Implementation [[OM-XML]]</td>
</tr>
<tr>
<td><code>wml2</code></td>
<td>http://www.opengis.net/waterml/2.0</td>
<td>WaterML 2.0 Encoding Standard [[WaterML]]</td>
</tr>
<tr>
<td><code>xlink</code></td>
<td>http://www.w3.org/1999/xlink</td>
<td>XML Linking Language (XLink) Version 1.1 [[XLINK11]]</td>
</tr>
</tbody>
</table>
</section>
</section>
<section id="spatial-things-features-and-geometry">
<h2>Spatial Things, Features and Geometry</h2>
<p>The <a>feature</a> is the primary entity as described in spatial data standards <a href="http://www.opengeospatial.org">Open
Geospatial Consortium</a> (OGC) and the 19100 series of <a href="http://www.isotc211.org">ISO/TC 211</a> <a>Geographic information</a>/Geomatics. [[ISO-19101-1-2014]] defines a feature
as an: “abstraction of real world phenomena”.</p>
<p>This terse definition is a little confusing, so let’s unpack it.</p>
<p>Firstly, it talks about “real world phenomena”; that’s everything from highways to
helicopters, parking meters to postcode areas, water bodies to weather fronts and more.
These can be physical things that you can touch (e.g. a phone box) or an abstract concept
that has spatial <a>extent</a> (e.g. a postcode area). <a>Features</a> can even be fictional (e.g.
“Dickensian London”) and may even lack any concrete location information such as the
mythical Atlantis.</p>
<p>The key point is that these “features” are things that one talks about in the <a>universe
of discourse</a> — which is defined in [[ISO-19101-1-2014]] as the “view of the real or hypothetical world that includes
everything of interest”.</p>
<p>Secondly, the definition of <a>feature</a> talks about “abstraction”. Take the example of <a
href="https://www.trinityhouse.co.uk/lighthouses-and-lightvessels/eddystone-lighthouse">Eddystone Lighthouse</a>. A helicopter pilot
might see it as a “vertical obstruction” and be interested in attributes such as its height and
precise location. Whereas a sailor may see it as a “maritime navigation aid” and need
information about its light characteristic and general location. Depending on one’s set of
concerns, only a subset of the attributes of a given “real world phenomenon” are relevant.
In the case of Eddystone Lighthouse, we defined two separate “abstractions”. As is common
practice in many information modelling activities, the common sets of attributes for a given
“abstraction” are used to define <em>classes</em>. In the parlance of [[ISO-19101-1-2014]], such a class is known as “feature
type”. </p>
<aside class="note">
<p>Although the exact semantics differ a little, there is a good correlation between the
concept of “feature type” as defined in spatial data standards and the concept
of “class” defined in [[RDF-SCHEMA]]. The former is an information modelling construct that
binds a fixed set of attributes to an identified resource, whereas the latter defines the
set of all resources that share the same group of attributes.</p>
<p>When combined with the <a>open-world assumption</a> embraced by [[RDF-SCHEMA]] and the Web
Ontology Language (OWL) [[OWL2-OVERVIEW]], the set-based approach to classes provides more
flexibility when combining information from multiple sources. For example, the “Eddystone
Lighthouse” resource can be seen as <em>both</em> a “vertical obstruction” <em>and</em> a
“maritime navigation aid” as it meets the criteria for membership of both sets.
Conversely, this flexibility makes it much more difficult to build software applications
as there is no guarantee that an information resource will specify a given attribute. Web
standards such the Shapes Constraint Language [[SHACL]] are being defined to remedy this
issue.</p>
</aside>
<p>However, the term “feature” is also commonly used to mean a capability of a system, application or component. Also, in some domains and/or applications no distinction is made between "<a>feature</a>" and the corresponding real-world phenomena.</p>
<p>To avoid confusion, we adopt the term “<a>Spatial Thing</a>” throughout the remainder of this best practice document. “<a>Spatial thing</a>” is defined in [[W3C-BASIC-GEO]] as “Anything with spatial extent, i.e. size, shape, or position. e.g. people, places, bowling balls, as well as abstract areas like cubes”.</p>
<p>The concept of “<a>Spatial Thing</a>” is considered to include <em>both</em> "real-world phenomena" <em>and</em> their abstractions (e.g. “<a>feature</a>” as defined in [[ISO-19101-1-2014]]). Furthermore, we treat it as inclusive of other commonly used definitions; e.g. <strong>Feature</strong> from [[NeoGeo]], described as “A geographical feature, capable of holding spatial relations”.</p>
<aside class="note">
<p>A <a>Spatial Thing</a> may move. We must take care not to oversimplify our concept of <a>Spatial Thing</a> by assuming that it is equivalent to definitions such as <strong>Location</strong> (from [[DCTERMS]]) or <strong>Place</strong> (from [[SCHEMA-ORG]]), which are respectively described as “A spatial region or named place” and "Entities that have a somewhat fixed, physical extension".</p>
</aside>
<p>Looking more closely, it is important to note that <a>geometry</a> is typically a property of a <a>Spatial
Thing</a>.</p>
<!--<div class="issue" data-number="1118"></div>-->
<aside class="example" id="ex-eddystone-geometry" title="Eddystone Lighthouse geometry (encoded as GeoJSON [RFC7946])">
<pre>
{
“geometry”: {
"type": "Point",