I've used the following method which uses some custom programs written by Warren Glimpse of Proxityone (www.proximityone.com) Here's a breif description: Though there are many ways to develop such a file, here is one method. The UAC and geocode hierarchy to get to the block level are contained in the composite of Census 2000 UA TIGER/Line files 1, A, and I. The appropriate TIGER/Line files can be downloaded from the Census server and processed with the Proximity TGR2DBF software creating a dbase structured version for these three TLFs. Next use TGR2DBF to create a census block-to-UA/UC code equivalency file (BLKUA.DBF). Next acquire the county by census block shapefile(s) from the Proximity map files website. Use the Proximity Cen2Shp software to merge the UA/UC code from the BLKUA.DBF into the county by block shapefile dbf. The augmented shapefile is now ready to support a display (or data link) of census blocks by user selected UA/UC. View the results of this process for the Lawrence, Kansas metropolitan area at http://proximityone.com/urbrural.htm Goto: http://www.proximityone.com/cen2000.htm#tigerua for more details. Ben Mauldin Director of Research Central Midlands Council of Governments