1. Nebraska Cartograms;Agena,2002
2. OpenMap;Bbn,2002
3. An Algorithm to Construct Continuous Area Cartograms;Dougenik;Professional Geographer,1985
4. Area Cartograms: Their Use and Creation;Daniel,1996
5. ESRI Shapefile Technical Description, An ESRI White Paper, July 1998;Esri,1998