Plotting maps

Introduction

I decided to give up on plotting nice maps with grass. The ps.map function is very powerful, but hard to remember for my not-so-frequent use. R has great plotting capabilities, and of course it does maps. It has an easy grass interface. What else do you want (importing other GIS formats? Try rgdal). Plotting GIS data is very nicely implemented in the sp package, part of the spatial data in R project, but getting your plot the way you want is quite challenging.

Required packages

spgrass6 reads data from the GRASS database. Sp implements spplot and lattice is used to define the colours (trells.par.set).

  library(sp)
  library(spgrass6)
  library(lattice)

Procedure

Here's what I came up with:

      paute <- rast.get6("paute_z")
      colours <- topo.colors(1000) # if you want pretty topographic colours
      colours <- gray(c(rep(100,10),100:15)/100) # for greyscale colours
      trellis.par.set(sp.theme(regions=list(col = colours)))
      scale = list("SpatialPolygonsRescale", layout.scale.bar(height=0.1), offset = c(690000,9735000), scale = 20000, fill=c("transparent","black"))
      text1 = list("sp.text", c(690000,9740000), "0")
      text2 = list("sp.text", c(710000,9740000), "20 km")
      arrow = list("SpatialPolygonsRescale", layout.north.arrow(type=1), offset = c(698000,9720000), scale = 10000)
      spplot(paute,draw = T, colorkey=list(space="right", height=0.5), cuts=127,
             scales=list(draw=T), sp.layout=list(scale,text1,text2,arrow))

Good to know:

• cuts defines the number of colour intervals. The default is 15 and that's not really nice for continuous DEM images
• the colorkey options are part of levelplot {lattice} and are quite customizable

Results