How to overlay map layers (shp and csv) in R?

Question

This is a crosspost from stackoverflow. I know very little about GIS software and am doing all my mapping in R. Apologies in advance if this is too basic question. Let's say I have two shapefiles from different sources but with different attributes. Say, one is for adminstrative boundaries of Texas (boundaries.shp) and the other is for Texas rivers (rivers.shp). I also have a third file towns.csv showing the locations of towns within the state. After reading in the files, I can overplot town locations on the adimistrative boundaries in the maptools package:

plot(boundaries); points(towns$lon, towns$lat)

But how can I overlay all three? Surely there is an easy way of doing this?

Answer 1

The simplest way to overlay two plots might be using the add = TRUE option in plot. Here is an example with artificial data

# Load sp package for creating artificial data
library(sp)

# Create sample town points
towns <- data.frame(lon = sample(100), lat = sample(100))
towns <- SpatialPoints(towns)

# Create sample polygon grid
grd <- GridTopology(c(1,1), c(10,10), c(10,10))
polys <- as.SpatialPolygons.GridTopology(grd)

# Plot polygons
plot(polys)

# Add towns (in red colour)
plot(towns, add = TRUE, col = 'red')

Answer 2

PBSMapping should fit your needs. There's a tutorial at NCEAS. The code below is adapted from that tutorial. I'm making assumptions about your data btw. Please edit as appropriate for your situation.

library(PBSmapping)

#prepare towns
pts <- read.csv("towns.csv")
towns <- points(towns$lon, towns$lat)
# read in shapefiles 
rivers <- importShapefile("rivers.shp")
boundaries <- importShapefile("boundaries.shp")


# note that importShapefile reads the .prj file if it exists, but it
# does not adopt the proj4 format used by the above approaches
proj.abbr <- attr(boundaries, "projection") # abbreviated projection info
proj.full <- attr(boundaries, "prj") # full projection info
print(proj.abbr)
# [1] "LL"

# generate map using PBSmapping plotting functions
plotPolys(boundaries, projection=proj.abbr, border="gray",
    xlab="Longitude", ylab="Latitude")
addPoints(towns, pch=20, cex=0.8)
addLines(rivers, col="blue", lwd=2.0)