If plot = TRUE, a plot is made where the polygons selected from database, through the regions, xlim, and ylim arguments, are outlined (fill is FALSE) or filled (fill is TRUE) with the colors in col. The return value is a list with x, y, range, and names components. This object can be used as a database for successive calls to map and functions. If fill is FALSE, the x and y vectors are the coordinates of successive polylines, separated by NAs. If fill is TRUE, the x and y vectors have coordinates of successive polygons, again separated by NAs. Thus the return value can be handed directly to lines or polygon, as appropriate. After a call to map for which the projection argument was specified there will be a global variable .Last.projection containing information about the projection used. This will be consulted in subsequent calls to map which use projection = &rdquo,. Richard A. Becker, and Allan R. Wilks, 'Maps in S', AT&T Bell Laboratories Statistics Research Report [93.2], 1993. http://ect.bell-labs.com/sl/doc/93.2.ps Richard A. Becker, and Allan R. Wilks, 'Constructing a Geographical Database', AT&T Bell Laboratories Statistics Research Report [95.2], 1995. http://ect.bell-labs.com/sl/doc/95.2.ps inside-R.org is a collection of resources about the open-source R Project for the R Statistics Community. This site is sponsored by Revolution Analytics. Source.