These functions transform some classes provided by the package sp into a simple list that can be used by map().
SpatialPolygons2map(database, namefield=NULL)
SpatialLines2map(database, namefield=NULL)A SpatialPolygons or SpatialLines object.
The name of a data column in database to be used for naming the polygons (or lines). If it is a vector of names, these are all used and separated by a colon ':'. Not case sensitive. So if the database contains columns that only differ by case, you get a warning and namefield is not used at all.
A list with four components: x, y, names, range, similar to the return value of map(). This data can be used as a database for map(). The lines and polygons are separated by NA.
The 'map' list object only preserves co-ordinates and polygon names. All other information available in the original data is lost.
The option namefield is only taken into account if database is class Spatial[]DataFrame. namefield may be a vector of column names, e.g. to get polygons named as 'country:state'.
map,SpatialPolygons (in the sp library),
readShapePoly (in the maptools library)