RE: [CTPP] Some more points

Block group data is and always has been important to the public sector. It has been essential to my activities as a transportation planner over the years. I cannot speak for other areas, but there is nothing "accidental" about the geography of block groups in the areas in which I work. Perhaps this is due to my active interest and involvement in the delineation of all census statistical areas affecting my work. The necessity of meeting minimum goals of persons and households for the sake of statistical analysis does occasionally lead to somewhat arbitrary aggregations of small areas. The necessity of delineating the block group boundaries prior to the actual census does occasionally lead to odd-looking results, especially in rapidly developing or redeveloping areas. Errors made by the Bureau of the Census in field review, in digitizing, or in geocoding are the only cause of "accidental" geography in my experience. For the 1990 census, the Bureau would not allow local entities to demand corrections to Bureau errors below the Census Tract level. In 2000, they are allowing us to demand corrections that affect block groups, but not individual blocks. (My metropolitan area had about half a mile of a major drainage feature eliminated during field review. The Bureau admitted it was their mistake but would not restore the block boundary.) In short, I'll fight over any decisions that diminish my flexibility in performing demographic analyses and would encourage other to do the same. Robert R. Allen, AICP Transportation Planning Director Abilene Metropolitan Planning Organization ph.: 915-676-6243 fax: 915-676-6242 Excerpt from Original Message----- From: owner-ctpp-news(a)chrispy.net [mailto:owner-ctpp-news@chrispy.net]On Behalf Of Patty Becker Sent: Sunday, January 27, 2002 12:04 PM To: ctpp-news(a)chrispy.net Subject: [CTPP] Some more points I am skeptical about block group data. They have never been very reliable anyhow, and are mostly important to the private sector because they permit more precise aggregation in what I call radius analyses (1 mile circle, three mile circle, etc.) The long form data at the individual block group level have very high sampling and non-sampling error rates. In addition, block groups are largely "accidental" geography, because the lines between them are most often arbitrary and not based on any real-life criteria. Tracts (and TAZs), on the other hand, are deliberately drawn to meet local criteria, or they should be. I think it would serve us all better to refer to TAZs as tract-equivalents rather than block-group equivalents. In areas without high employment density, that's what they are. I don't think a fight over block group data will serve anyone well as this point.