I'm using ggmap to grab Washington DC and I have a shapefile that I downloaded from here:
library(ggplot2)library(ggmap)library(maptools)dc = get_map(location = 'DC', zoom = 12)nhbds = readShapePoly("Census_Tracts_-_2010.shp")ggmap(dc) + geom_polygon(aes(x = long, y = lat, group = group)...