Remove border lines in ggplot map/choropleth

Question

I would like to remove the lines between regions of a choropleth generated in ggplot. My question is motivated by a very large map with very very small regions

Answer 1

I can confirm it's specific to the Mac. Was just trying to do the same and 'colors=NA' has no visible effect in R Studio on a Mac, the borders still show. Just loaded the project on Windows and the borders are gone.

For reference, my set-up: Mac is running R Studio 0.98.1074 on Mac OS X 10_10_1 (Yosemite). Windows is running R Studio 0.98.1073 on Windows 7.