Prion Prion - 3 months ago 22
R Question

Mapping specific States and Provinces in R

I'm trying to use R to generate a figure with sample localities for my FieldBio project. So far, I've been able to map the US states I want, to map Canada (national border), to overlay these two maps; what I'd like to do, though, is to map the following states/provinces specifically, excluding the others:
California
Nevada
Utah
Colorado
Wyoming
Montana
Idaho
Washington
Oregon
British Columbia
Alberta

Here is the code I've been using so far:

>map('state', region = c('california', 'nevada', 'utah', 'colorado', 'wyoming', 'montana', 'idaho', 'oregon', 'washington'), xlim=c(-130,-90), ylim=c(30,60), fill=TRUE, col="gray95")

>map("worldHires","Canada", xlim=c(-130,-90), ylim=c(30,60), col="gray95", fill=TRUE, add=TRUE)


This produces a map with the desired states, but canada as a country (cut off at the delimitors I set).

Is there a way to do only the provinces I want? I think I know how to plot the points (I have them as a .csv with lat and long data) on top of this afterward.

I realize that (R: creating a map of selected Canadian provinces and U.S. states) is pretty similar, but I'm getting a little lost in the code for that particular example, and I don't need to highlight anything specific.

Thanks

Answer

Like this?

library(raster)
states    <- c('California', 'Nevada', 'Utah', 'Colorado', 'Wyoming', 'Montana', 'Idaho', 'Oregon', 'Washington')
provinces <- c("British Columbia", "Alberta")

us <- getData("GADM",country="USA",level=1)
canada <- getData("GADM",country="CAN",level=1)

us.states <- us[us$NAME_1 %in% states,]
ca.provinces <- canada[canada$NAME_1 %in% provinces,]

us.bbox <- bbox(us.states)
ca.bbox <- bbox(ca.provinces)
xlim <- c(min(us.bbox[1,1],ca.bbox[1,1]),max(us.bbox[1,2],ca.bbox[1,2]))
ylim <- c(min(us.bbox[2,1],ca.bbox[2,1]),max(us.bbox[2,2],ca.bbox[2,2]))
plot(us.states, xlim=xlim, ylim=ylim)
plot(ca.provinces, xlim=xlim, ylim=ylim, add=T)

So this uses the getData(...) function in package raster to grab the SpatialPolygonDataFrames for US states and Canadian provinces from the GADM site. Then it extracts only the states you want (notice that the relevant attribute table field is NAME_1 and the the states/provinces need to be capitalized properly). Then we calculate the x and y-limits from the bounding boxes of the two (subsetted) maps. Finally we render the maps. Note the use of add=T in the second call to plot(...).

And here's a ggplot solution.

library(ggplot2)
ggplot(us.states,aes(x=long,y=lat,group=group))+
  geom_path()+
  geom_path(data=ca.provinces)+
  coord_map()

The advantage here is that ggplot manages the layers for you, so you don't have to explicitly calculate xlim and ylim. Also, IMO there is much more flexibility in adding additional layers. The disadvantage is that, with high resolution maps such as these (esp the west coast of Canada), it is much slower.