I'm trying to create a map of US shale basins and I'm very new to creating maps. I have downloaded the shapefiles from the US Energy Information Administration (EIA). I have also, been able to created a basic map with the bases plotted (please see code below). I would like to add labels etc. to this map. I believe these would be in the other files downloaded outside the shapefile.
library(maps)
map("state")
shapLocation<- "C:/shapfile/shalegasbasin/"
pcontorta <- readShapePoly(paste(shapLocation,"US_ShaleBasins_EIA_May2011.shp",sep=""))
plot(pcontorta, add=TRUE, col=adjustcolor("black", alpha.f = 0.6), border=FALSE)
Shapefile from: http://www.eia.gov/maps/layer_info-m.cfm
Description of a shapefile: http://en.wikipedia.org/wiki/Shapefile
Best Answer
Take a look at ?text. You can place the labels using the polygon coordinates which will return approximate polygon centroids.