Ed: I'm thinking of converting all of my travel analysis zones to hexagons. Either that or 10 meter square grid cells. ;-) Seriously, I never thought of county boundaries as an issue in TAZ development. It would be a puzzling aggregation problem if a local TAZ "straddled" two-or-more counties! So, the most common model that MPOs will probably follow is a nesting model: using Census blocks as the lowest common denominator and building up from that basis. Ideally everything will nest on everything else for all purposes (e.g., block groups, census tracts, city boundaries, voting precincts, zip codes, TAZs, counties, telephone area codes, minor civil divisions, states). That's not likely to occur. The most important nesting criteria for me would be: TAZ, census tract, city, county, region. In this particular criteria, I would sacrifice city boundaries given the incorporated / unincorporated geographic mishmash we have here in California. I'll raise two issues related to TAZ-UP and TAZ development: 1. When will we need to get this work done? 2. What is the "smallest size" travel zone that can be developed, in terms of the total population, or workers-at-work in the proposed TAZ? Perhaps our beltway friends can answer these questions? That's about all for now. Chuck Purvis, MTC ******************************************************* ** ON VACATION: OCTOBER 3 - 31, 1998 ***************** e-mail: cpurvis(a)mtc.ca.gov Chuck Purvis, AICP Senior Transportation Planner/Analyst, Planning Section Metropolitan Transportation Commission 101 Eighth Street, Oakland, CA 94607-4700 (510) 464-7731 (voice) (510) 464-7848 (fax) WWW: http://www.mtc.ca.gov/ MTC DataMart & InfoMart: http://www.mtc.ca.gov/facts_and_figures/datamart.htm MTC FTP Site: ftp://ftp.abag.ca.gov/pub/mtc/planning/ Personal WWW: http://home.earthlink.net/~clpurvis/ *******************************************************