[R-sig-Geo] Problem with polygon holes and islands

[Ian Reeve]

Problem with census tracts with holes and census tracts that are collections of islands not plotting, posted to R-sig-Geo on 5 Mar 2011, has been resolved.  checkPolygonsHoles() fixed the problem, both for holes and collections of islands (thanks, Roger).  The MIF files containing this census tract data came from the Australian Bureau of Statistics (ABS) website.  Roger notes that:

"ABS has a history of generating odd files - its shapefiles from some years ago used a very non-standard method of adding null geometries to insert non-localised data into the DBF file. This is why readOGR has a dropNULLGeometries= argument, and readShapePoly() in maptools has delete_null_obj= and retrieve_ABS_null= arguments (the ABS is the same organisation, not the mathematical function!). I guess they find these oddities helpful in some way in-house."

Ian Reeve
University of New England
Armidale, NSW