zross/ggplot_map.R

## ggplot_map.R
# In response to a question on our ggplot2/mapping post
# (http://zevross.com/blog/2014/07/16/mapping-in-r-using-the-ggplot2-package/)
# this is an example of using ggplot2's built-in
# borders() function and an external shapefile

# The shapefile used in that blog post is a projected shapefile
# but by default the borders() function uses unprojected
# boundaries so you will need to "unproject" the shapefile
# for the borders to match. An alternative would be to assign
# a projection with map() arguments

# The shapefile is from:
# http://www.nyc.gov/html/dcp/html/bytes/districts_download_metadata.shtml


library(rgdal)

# this is projected and won't match up
# with ggplot2's default "border" layer
cnty<-readOGR("nybb.shp", layer="nybb")
proj4string(cnty) # see projection

# "unproject" this -- assign unprojected geographic coord system
# wgs84 would be nearly equivalent but we use nad83
cnty<-spTransform(cnty, CRS("+proj=longlat +datum=NAD83"))

# now it matches
library(ggplot2)
library(maps)
data(us.cities)
capitals <- subset(us.cities, capital == 2 & country.etc=="NY")
ggplot(capitals, aes(long, lat)) +
  borders('state', region = c('new york')) +
  geom_point(aes(size = pop)) +
  geom_polygon(data=cnty, aes(long,lat, group=group))
	# In response to a question on our ggplot2/mapping post
	# (http://zevross.com/blog/2014/07/16/mapping-in-r-using-the-ggplot2-package/)
	# this is an example of using ggplot2's built-in
	# borders() function and an external shapefile

	# The shapefile used in that blog post is a projected shapefile
	# but by default the borders() function uses unprojected
	# boundaries so you will need to "unproject" the shapefile
	# for the borders to match. An alternative would be to assign
	# a projection with map() arguments

	# The shapefile is from:
	# http://www.nyc.gov/html/dcp/html/bytes/districts_download_metadata.shtml


	library(rgdal)

	# this is projected and won't match up
	# with ggplot2's default "border" layer
	cnty<-readOGR("nybb.shp", layer="nybb")
	proj4string(cnty) # see projection

	# "unproject" this -- assign unprojected geographic coord system
	# wgs84 would be nearly equivalent but we use nad83
	cnty<-spTransform(cnty, CRS("+proj=longlat +datum=NAD83"))

	# now it matches
	library(ggplot2)
	library(maps)
	data(us.cities)
	capitals <- subset(us.cities, capital == 2 & country.etc=="NY")
	ggplot(capitals, aes(long, lat)) +
	borders('state', region = c('new york')) +
	geom_point(aes(size = pop)) +
	geom_polygon(data=cnty, aes(long,lat, group=group))