Preface

Last updated: 2020-09-28 17:43:24

0.1 What is R?

R is a programming language and environment, originally developed for statistical computing and graphics. As of October 2019, there are ~15,000 R packages in the official repository CRAN1.

Notable advantages of R are that it is a full-featured programming language, yet customized for working with data, relatively simple and has a huge collection of over 100,000 functions from various areas of interest.

R’s popularity has been steadily increasing in recent years (Figures 0.10.3).

Stack Overflow Trend for the 'r' question tag^[https://insights.stackoverflow.com/trends?tags=r]

Figure 0.1: Stack Overflow Trend for the ‘r’ question tag2

IEEE Language Rankings 2019^[https://spectrum.ieee.org/computing/software/the-top-programming-languages-2019]

Figure 0.2: IEEE Language Rankings 20193

Proportion of research papers citing R^[https://www.nature.com/news/programming-tools-adventures-with-r-1.16609]

Figure 0.3: Proportion of research papers citing R4

A brief overview of the capabilities and packages for several domains of R use, are available in the “CRAN Task Views” (Figure 0.4).

CRAN Task Views^[http://www.maths.lancs.ac.uk/~rowlings/R/TaskViews/]

Figure 0.4: CRAN Task Views5

0.2 R and analysis of spatial data

0.2.1 Introduction

Over time, there was an increasing number of contributed packages for handling and analyzing spatial data in R. Today, spatial analysis is a major functionality in R. As of October 2019, there are 194 packages6 specifically addressing spatial analysis in R.

Books on Spatial Data Analysis with R

Figure 0.5: Books on Spatial Data Analysis with R

Some important events in the history of spatial analysis support in R are summarized in Table 0.1.

Table 0.1: Significant events in the history of R-spatial
Year Event
pre-2003 Variable and incomplete approaches (MASS, spatstat, maptools, geoR, splancs, gstat, …)
2003 Consensus that a package defining standard data structures should be useful; rgdal released on CRAN
2005 sp released on CRAN; sp support in rgdal
2008 Applied Spatial Data Analysis with R, 1st ed.
2010 raster released on CRAN
2011 rgeos released on CRAN
2013 Applied Spatial Data Analysis with R, 2nd ed.
2016 sf released on CRAN
2018 stars released on CRAN
2019 Geocomputation with R (https://geocompr.robinlovelace.net/)
2021(?) Spatial Data Science (https://www.r-spatial.org/book/)

The question that arises here is: can R be used as a Geographic Information System (GIS), or as a comprehensive toolbox for doing spatial analysis? The answer is definitely yes. Moreover, R has some important advantages over traditional approaches, mainly software with graphical user interfaces, like ArcGIS or QGIS.

General advantages of Command Line Interface (CLI) software include:

  • Automation—Doing otherwise unfeasible repetitive tasks
  • Reproducibility—Precise control of instructions to the computer

Moreover, specific strengths of R as a GIS are:

  • R capabilities in data processing and visualization, combined with dedicated packages for spatial data
  • A single environment encompassing all analysis aspects—acquiring data, computation, statistics, visualization, Web, etc.

Nevertheless, there are situations when other tools are needed:

  • Interactive editing or georeferencing (but see mapedit package)
  • Unique GIS algorithms (3D analysis, label placement, network routing, splitting lines at intersections, etc.)
  • Data that cannot fit in RAM (but R can connect to spatial databases7)

0.2.2 Input and output of spatial data

Reading spatial layers from a file into an R data structure, or writing the R data structure into a file, are handled by external libraries:

  • GDAL/OGR is used for reading/writing vector and raster files, with sf and stars
  • PROJ is used for handling CRS, in both sf and stars
  • Working with specialized formats, e.g., HDF with gdalUtils or NetCDF with ncdf4

Package sf combined with RPostgreSQL can be used to read from, and write to, a PostGIS spatial database:

0.2.3 sf: Processing Vector Layers

GEOS is used for geometric operations on vector layers with sf:

  • Numeric operators—Area, Length, Distance…
  • Logical operators—Contains, Within, Within distance, Crosses, Overlaps, Equals, Intersects, Disjoint, Touches…
  • Geometry generating operators—Centroid, Buffer, Intersection, Union, Difference, Convex-Hull, Simplification…
Buffer function

Figure 0.6: Buffer function

0.2.4 stars: Processing Rasters

Geometric operations on rasters can be done with package stars:

  • Accessing cell values—As matrix / array, Extracting to points / lines / polygons
  • Raster algebra—Arithmetic (+, -, …), Math (sqrt, log10, …), logical (!, ==, >, …), summary (mean, max, …), Masking
  • Changing resolution and extent—Cropping, Mosaic, Resampling, Reprojection
  • Transformations—Raster <-> Points / Contour lines / Polygons

0.2.5 geosphere: Geometric calculations on longitude/latitude

Package geosphere implements spherical geometry functions for distance- and direction-related calculations on geographic coordinates (lon-lat)

Points on Great Circle

Figure 0.7: Points on Great Circle

Visualizing Facebook Friends with `geosphere`^[http://paulbutler.org/archives/visualizing-facebook-friends/]

Figure 0.8: Visualizing Facebook Friends with geosphere8

0.2.6 gstat: Geostatistical Modelling

Univariate and multivariate geostatistics:

  • Variogram modelling
  • Ordinary and universal point or block (co)kriging
  • Cross-validation
Predicted Zinc concentration, using Ordinary Kriging

Figure 0.9: Predicted Zinc concentration, using Ordinary Kriging

0.2.7 spdep: Spatial dependence modelling

Modelling with spatial weights:

  • Building neighbor lists and spatial weights
  • Tests for spatial autocorrelation for areal data (e.g., Moran’s I)
  • Spatial regression models (e.g., SAR, CAR)
Neighbours list based on regions with contiguous boundaries

Figure 0.10: Neighbours list based on regions with contiguous boundaries

0.2.8 spatstat: Spatial point pattern analysis

Techniques for statistical analysis of spatial point patterns, such as:

  • Kernel density estimation
  • Detection of clustering using Ripley’s K-function
  • Spatial logistic regression
Distance map for the Biological Cells point pattern dataset

Figure 0.11: Distance map for the Biological Cells point pattern dataset

0.2.10 ggplot2, ggmap: Visualization

London cycle hire journeys with `ggplot2`^[http://spatial.ly/2012/02/great-maps-ggplot2/]

Figure 0.13: London cycle hire journeys with ggplot210

Crime density by day with `ggplot2`

Figure 0.14: Crime density by day with ggplot2

0.2.11 leaflet, mapview: Web mapping

Packages leaflet and mapview provide methods to produce interactive maps using the Leaflet JavaScript library.

Package leaflet gives more low-level control. Package mapview is a wrapper around leaflet, automating addition of useful features:

  • Commonly used basemaps
  • Color scales and legends
  • Labels
  • Popups

Function mapview produces an interactive map given a spatial object:

  • zcol="..." specifies the attribute used for symbology
  • legend=TRUE adds a legend
Intractive map made with `mapview`

Figure 0.15: Intractive map made with mapview

0.3 Other materials

0.3.1 Books

  • Model-based Geostatistics (2007)
  • A Practical Guide to Geostatistical Mapping (2009)
  • Spatial Data Analysis in Ecology and Agriculture using R (2012)
  • Learning R for Geospatial Analysis (2014)
  • Applied Spatial Data Analysis with R (1st ed. 2008, 2nd ed. 2013)
  • Hierarchical Modeling and Analysis for Spatial Data (1st ed. 2003, 2nd ed. 2014)
  • An Introduction to R for Spatial Analysis and Mapping 1st ed. 2015, 2nd ed. 2018)
  • Spatial Point Patterns: Methodology and Applications with R (2015)
  • Displaying Time Series, Spatial, and Space-Time Data with R (1st ed. 2014, 2nd ed. 2018)
  • Predictive Soil Mapping with R (2019)
  • Geocomputation with R (2019)
  • Spatial Data Science (2021?)

0.3.2 Papers

  • Pebesma, E., Bivand, R. S. (2005). Classes and Methods for Spatial Data: the sp Package. R news, 5(2), 9-13. [PDF]
  • Pebesma, E. (2018). Simple Features for R: Standardized Support for Spatial Vector Data. The R Journal, 10(1):439-446. [PDF]