I created an R package to load NYC Borough boundaries that is available on github.

#load and use the map
devtools::install_github("zachcp/nycmaps")
libary(nycmaps)
library(maps)
map(database="nyc")

A few notes

1. check the data-raw directory for a Makefile on Downloading and converting the geojson into the R-binary format
2. Most regions/islands have been names but I may be missing some.
3. Many of the Jamaica Bay Islands are not included (I took them all out and then added back the big ones around Cross Bay Boulevard)
4. when loading this sets a /GlobalEnd defining where the map files live. To be incorporated in Maps or included in CRAN this is a no-no but I don’t a better way.