Ed, I'm not quite sure what is meant by the following statement from your messge below: "All of these geographies could be aggregated to PUMAs if desired by the MPO/State. And of course, all zones would have to nest within counties." I assume by "all of these geographies" you mean tracts and block groups. If so, it is correct that tracts and block groups generally will aggregate to PUMAs. "Generally" is the operative word here because PUMAs generally are defined using either tracts or counties as "building blocks." Since block groups nest within tracts, which nest within counties, there usually is a nice, neat relationship between block groups, tracts, counties, and PUMAs. The exception is when a PUMA follows the boundary of a principal city of a metropolitan statistical area. In that situation, block groups and tracts will not aggregate to the PUMA. This situation tends to be the exception rather than the rule. The Census Bureau has not developed plans for updating PUMA boundaries for 2010. That said, at this time I don't foresee any substantive changes to the way in which PUMAs are delineated. Mike Ratcliffe ______________________________________ Michael R. Ratcliffe Chief, Geographic Standards and Criteria Branch Geography Division U.S. Census Bureau 301-763-8977 michael.r.ratcliffe(a)census.gov ed christopher <edc(a)berwyned.com Sent by: ctpp-news maillist ctpp-news-bounces <ctpp-news(a)chrispy.net> @chrispy.net cc Subject 03/07/2007 01:38 [CTPP] TAZ Update PM Last October Elaine Murakami posted an email to this listserve (http://www.chrispy.net/pipermail/ctpp-news/2006-October/001517.html) updating folks on the discussions that are underway between FHWA and the Census Bureau (CB) Geography Division regarding the definition of new TAZs to be used for the 5-year special tabulation of the ACS data. Since that time further progress has been made. It looks like MPOs and State DOTs would be working on their TAZs toward the end of 2008 and early 2009 with TAZs being submitted in the middle of 2009. This is important because many areas are already preparing their work programs to cover this time frame. Exactly, how much work will be involved is not yet known. The plan (desire) is to use a GIS-based approach similar to that used for the TAZ definition for the CTPP2000. We would like a system that does not require special licensing of GIS software and is user friendly much like the TAZ-UP effort used for CTPP2000. As an historic note, the TAZ-UP program for CTPP2000 was developed as an add-on to ArcView 3.1 and required users to have a licensed version of ArcView. Currently, FHWA staff has asked the CB to plan for the software to create three levels of TAZs that nest within each other. The smallest is a base TAZ that would be similar to the traditional “small area geography” TAZs used in 2000 and 1990 . The next size, or medium sized TAZs, would be aggregates of the base TAZs (about 4,000 population) and the larger size (about 20,000 population) TAZs would be aggregates of the medium TAZs. This is very akin to Blocks being aggregated to Block Groups and then Block Groups being aggregated to Tracts. All of these geographies could be aggregated to PUMAs if desired by the MPO/State. And of course, all zones would have to nest within counties. There are still quite a few details to be fleshed out but for now it is important to recognize that some staff time on the part of the MPOs and States will be required if an area wishes to define TAZs. Updates to these activities will be posted on this listserve and in quarterly “Status Report” newsletter which can be found online at http://www.trbcensus.com/ or http://www.dot.gov/ctpp -- Ed Christopher Resource Center Planning Team Federal Highway Administration 19900 Governors Drive Olympia Fields, Illinois 60461 708-283-3534 (V) 708-574-8131 (cell) 708-283-3501 (F) _______________________________________________ ctpp-news mailing list ctpp-news(a)chrispy.net http://www.chrispy.net/mailman/listinfo/ctpp-news