Hi folks, If perhaps you're interested in the opinion of someone who knows more about census geography/data than about TAZs specifically: I think TAZs should nest to census tracts (which by definition will then follow county lines). Tracts need more than one TAZ where there are employment concentrations; more than one tract may constitute a TAZ when you're in homogenous residential areas within a municipality. I also think you should be worrying, or at least thinking, about the sampling errors involved in small population TAZs. Block group data, even with an average of 600 housing units, are too small to deliver decent data. This is especially true for the journey to and place of work data, which have additional non-response errors beyond the overall sampling and non-response errors for the long form. I have never reported or relied on census-based place of work counts unless there were at least 1000 workers in the geographic area being reported. My guess is that census will end up permitting data to be delivered on a CTPP/UTPP for whatever geography you draw; disclosure will probably not be a problem unless you start using the finely drawn race/ethnic groups which will now be possible. But just because you can get the data doesn't mean the numbers are worth anything. One final word--at the risk of incurring the wrath of at least some of you--I really don't see why it's so important to maintain complete comparability from one set of TAZs to the next. The most important thing, I would think, is to have TAZs which reflect the current land use/population distribution/etc. to make good forecasts. If they need changing for whatever reason, they should be changed. Patty Becker ============================= Patricia C. (Patty) Becker 313/535-2077 APB Associates/SEMCC FAX 313/535-3556 17321 Telegraph #204 Home 248/355-2428 Detroit, MI 48219 pbecker(a)umich.edu