Regarding my query about ways to do comparative analysis at the tract level using 1990 vs. 2000 tracts, I received several very useful replies. To sum: · The tract comparability table for 1990-2000 tracts has not yet been released; best contact person is Kathy Miller at the Census (301-457-1128) · People are using a workaround involving Two-Theme Analyst (http://gis.esri.com/arcscripts/details.cfm?CFGRIDKEY=1391963324), an AV Extension which they use to aggregate 1990 block-level data into 2000 tracts Many Thanks to: Lisa Vorderbrueggen, David Herzog, Andy Crain, Andy Moncla and Mike Furlough Individual responses: What I and a bunch of other reporters have been doing is using an ArcView extension called Two-Theme Analyst to aggregate the 1990 block-level data into the 2000 tracts. It seems to work well. Two-Theme Analyst will take your 1990 data, joined to the 1990 block shape, file and assign it to the appropriate 2000 tract. If a block overlaps onto two tracts, Two Theme Analyst will assign a percentage of the population, based on the size of the block within the tract. As you've discovered, the tract comparability table for 1990-2000 tracts has not yet been released by the Census Bureau. I and many other journalists as a result created our own workaround. We used an extension called Two-theme Analyst (http://gis.esri.com/arcscripts/details.cfm?CFGRIDKEY=1391963324) to aggregate 1990 block-level data into 2000 tract boundaries. Aggregating 1990 block data meant that most of the aggregation was logical (ie, the 1990 blocks were contained entirely within 2000 tracts and could be counted 100 percent) and there was very little assignment of values based on area (done where a 1990 block crossed a 2000 tract line, and which could prove a problem if, for example, all the people in a block split in half by a tract lived in one corner, in which case they'd incorrectly be counted half in the tract and half in the adjacent tract). It's the best solution available until the Census releases a tract comparison table. One way to make comparisons between 1990 and 2000 is to load 1990 census block group data into ArcView, overlay 2000 tract boundaries and run two-themed analyst on the data of your choice. This allows you to compare the same ground in 1990 with 2000. In our case, we did it on population which had the effect of showing the outer ring suburbs in the Bay Area growing at a rapid rate. I recently spoke with someone at the Census Bureau who said this file would be out soon. However, my notes don't say when. I have found that if you write to the Bureau by Email they are very quick to respond and quite helpful. For 2000 products, they seem to want us to write to webmaster@census.gov. The comparability file has not yet been released. Kathy Miller at the Census (301-457-1128) is a good contact and give you a good time frame for the comparability file's release. James L. Sadd Chair, Environmental Science and Studies Program Associate Professor of Environmental Science Occidental College 1600 Campus Road Los Angeles, CA 90041 voice (323) 259-2518 fax (323) 259-2704 jsadd@oxy.edu