----------------------------Original message---------------------------- Does anyone know whether there exists a digital list showing the relationship between 1960 and 1970 census tract numbers for Chicago? The _much_ larger issue is: Is anyone out there working on (or have available) historical census boundary files for the United States in a familiar GIS format? What one would want would be not only boundary files for each decade but census data for succeeding decades consolidated to earlier decade boundaries--plus correspondence lists when tract numbers or other geocodes have changed. In other words, Tiger and summary tape files for each decade--plus decade-by-decade data for succeeding decades. Here at the U of C Map Collection, we created boundary files for Northeastern Illinois/Northwestern Indiana for 1980, including some 1990 data consolidated to 1980 boundaries. It was a lot of work--not the sort of thing that should be done twice. Thanks for any help. Chris Winters University of Chicago Library Internet: [log in to unmask]