This database produces a map of the United States mainland generated from US Department of the Census data (see the reference).
The data file is merely a character string which
specifies the name of an environment variable which contains the
base location of the binary files used by the map drawing functions.
This environment variable (
R_MAP_DATA_DIR for the datasets in the
maps package) is set at package load time if it does not
already exist. Hence setting the environment variable before loading
the package can override the default location of the binary datasets.
Richard A. Becker, and Allan R. Wilks, "Maps in S", AT\&T Bell Laboratories Statistics Research Report [93.2], 1993.
Richard A. Becker, and Allan R. Wilks, "Constructing a Geographical Database", AT\&T Bell Laboratories Statistics Research Report [95.2], 1995.
US Department of Commerce, Census Bureau, County Boundary File, computer tape, available from Customer Services, Bureau of the Census, Washingdon DC 20233.