Harlan Onsrud Gilberto Câmara James Campbell Narnindi Sharad Chakravarthy Public Commons of Geographic Data: Research and Development Challenges. 223-238 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3234&spage=223 2004 conf/giscience/2004 GIScience db/conf/giscience/giscience2004.html#OnsrudCCC04