Census Tract Boundaries For the 1991 and 1996 files gca535ct.e00 and gct_535a.e00 the projection is *Geographic* (the *g* beginning the name of the file tells it) The datum is NAD27 NAD83 is been in use only since the 2001 geography was elaborated. (From email: January 11, 2002) Abreviation Product BFDF Block Face Data file CD_CSD Census Division and Census Subdivisions , reference map series CMA Census Metropolitain Areas, Aglomeration & Census Tracts, reference map series GAF Geography Attribute File COGG Complete On line Guide to Geography DBF Digital Boundary File DCF Digital Cartographic File EA Enumeration Areas , reference map series EACORR Enumeration Area Correspondence File data quality statement & record layout PCCF Postal Code Conversion File PCFR Postal Code / Federal Riding File PNMF Place Name Master File SI Street Index SNFAMF Street Network File - Area Master File SNFARC Street Network File - ArcInfo SSNF Skeletal Street Network File SUPPLEMN Enumeration Areas Linkage Errors on the 1991 Geo. Attrib.Data Base