Discrete Global Grids for R: Spatial Analysis Done Right
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README.md

dggridR: Discrete Global Grids for R

Spatial Analysis Done Right

You want to do spatial statistics, and it's going to involve binning.

Binning with a rectangular grid introduces messy distortions. At the macro-scale using a rectangular grid does things like making Greenland bigger than the United States and Antarctica the largest continent.

Mercator Projection

But this kind of distortion is present no matter what the resolution is; in fact, it shows up whenever you project a sphere onto a plane.

What you want are bins of equal size, regardless of where they are on the globe, regardless of their resolution.

dggridR solves this problem.

dggridR builds discrete global grids which partition the surface of the Earth into hexagonal, triangular, or diamond cells, all of which have the same size. (There are some minor caveats which are detailed in the vignettes.)

Discrete Global Grid in use

(Naturally, you can use much smaller cells than those shown in the image above.)

This package includes everything you need to make spatial binning great again.

Many details and examples are included in the vignette.

Installation

dggridR is available from CRAN via:

install.packages('dggridR')

If you want your code to be as up-to-date as possible, you can install it using:

library(devtools) #Use `install.packages('devtools')` if need be
install_github('r-barnes/dggridR', vignette=TRUE)

Show me some code

Okay.

Your analysis could be as easy as this:

library(dggridR)
library(dplyr)

#Construct a global grid with cells approximately 1000 miles across
dggs          <- dgconstruct(spacing=1000, metric=FALSE, resround='down')

#Load included test data set
data(dgquakes)

#Get the corresponding grid cells for each earthquake epicenter (lat-long pair)
dgquakes$cell <- dgtransform(dggs,dgquakes$lat,dgquakes$lon)

#Get the number of earthquakes in each equally-sized cell
quakecounts   <- dgquakes %>% group_by(cell) %>% summarise(count=n())

Show me more examples!

In R, typing

vignette('dggridR')

will bring up many examples.

But I want higher resolution grids than that

Many different grid resolutions are available for many different grids. The following chart shows the number of cells, their area, and statistics regarding the spacing of their center nodes for the ISEA3H grid type.

Res Number of Cells Cell Area (km^2) Min Max Mean Std
1 32 17,002,187.39080 4,156.18000 4,649.10000 4,320.49000 233.01400
2 92 5,667,395.79693 2,324.81000 2,692.72000 2,539.69000 139.33400
3 272 1,889,131.93231 1,363.56000 1,652.27000 1,480.02000 89.39030
4 812 629,710.64410 756.96100 914.27200 855.41900 52.14810
5 2,432 209,903.54803 453.74800 559.23900 494.95900 29.81910
6 7,292 69,967.84934 248.80400 310.69300 285.65200 17.84470
7 21,872 23,322.61645 151.22100 187.55000 165.05800 9.98178
8 65,612 7,774.20548 82.31100 104.47000 95.26360 6.00035
9 196,832 2,591.40183 50.40600 63.00970 55.02260 3.33072
10 590,492 863.80061 27.33230 35.01970 31.75960 2.00618
11 1,771,472 287.93354 16.80190 21.09020 18.34100 1.11045
12 5,314,412 95.97785 9.09368 11.70610 10.58710 0.66942
13 15,943,232 31.99262 5.60065 7.04462 6.11367 0.37016
14 47,829,692 10.66421 3.02847 3.90742 3.52911 0.22322
15 143,489,072 3.55473 1.86688 2.35058 2.03789 0.12339
16 430,467,212 1.18491 1.00904 1.30335 1.17638 0.07442
17 1,291,401,632 0.39497 0.62229 0.78391 0.67930 0.04113
18 3,874,204,892 0.13166 0.33628 0.43459 0.39213 0.02481
19 11,622,614,672 0.04389 0.20743 0.26137 0.22643 0.01371
20 34,867,844,012 0.01463 0.11208 0.14489 0.13071 0.00827

Credits

The code in the 'src' directory is based off of DGGRIDv6.2b by Kevin Sahr.

However, Richard Barnes has made some significant alterations. These include:

  • Replacement of gpclib with clipper, thus making DGGRID into FLOSS software available for both commerical and non-commerical use without restriction
  • Restructuring and simplifying all of the makefiles to enable compilation in R
  • Direct inclusion of the shapelib library
  • Addition of the SEQTOPOLY option under the GENERATE_GRID faculty
  • Alterations that enable the code to be compiled under GCC6
  • Alterations that make the code ISO C conformant
  • Alterations to resolve -pedantic and -Wall warnings

The package relies on several libraries, as noted in the Licensing section below.

Licensing

This package uses the following libraries:

  • clipper: The clipper library has been released under the Boostv1 license by Angus Johnson

  • dggrid: Kevin Sahr has released dggrid as a "public domain software program"

  • proj4lib: Gerald Evenden has released this code into the public domain. More recent versions of the library, not used here, are under an MIT-style license.

  • shapelib: Frank Warmerdam has released shapelib under an MIT-style license. There is also an LGPL licensing option which I have chosen not to use.

This package, and all code and documentation not otherwise mentioned above (essentially anything outside the src/ directory of this package) are released under the MIT (Expat) license, as stated in the LICENSE file. The LICENCE file exists for use with CRAN.

Disclaimer

This package should operate in the manner described here, in the package's main documentation, and in Kevin Sahr's dggrid documentation. Unfortunately, none of us are paid enough to make absolutely, doggone certain that that's the case. That said, if you find bugs or are seeking enhancements, we want to hear about them.

Citing this Package

Please cite this package as:

Richard Barnes (2016). dggridR: Discrete Global Grids for R. https://github.com/r-barnes/dggridR.