Incoming query to CTPP:
1. The Size of TAZ : In your TAZ-UP manual(4-6) we have been told that "there
are no minimum size criteria for TAZs for CTPP 2000 . ... however, that census
data may be suppressed to protect confidentiality if a TAZ is too small."
What do you mean "too small"? Could your give us a number (or a range) of
RESIDENTS and WORKERS refers to this definition?
You provided us 1990 historical mean number/range for RESIDENTS and WORKERS
per TAZ. It seems that we have great flexibility to set our own criteria for
defining the size of TAZs for CTPP 2000.
To avoid possible problems caused by this ambiguity, we prefer to have a clear
criteria number or range from you.
Do you have any suggestion for us to dealing with those TAZs that
have mixed land use? Another words, if a TAZ has both RESIDENTS and WORKERS in
it, should we use RESIDENTS or WORKERS to define our TAZs?
Response from Elaine Murakami, FHWA
The text on page 4-6 of the TAZ-UP manual is the best we can do. There is NO
strict criteria. What is NOT going to work is for each block to be it's own
TAZ. However, there are cases in large urban downtown areas where a large
building (let's say it has more than 1000 workers, but no residents) is one
block and it makes sense for this block to be its own TAZ.
There may be special situations where a TAZ has less than 400 workers or 400
residents, but we would use 400 as a target MINIMUM. Preferably, the minimum
should be closer to 600, since we are planning for the CTPP tabulations to
have 2-way and 3-way cross tabulations, and if there are too many cells in the
cross-tab, we will run into a greater likelihood that data could be
Areas with mixed land use, I would still use 400 as the minimum for either
workers or residents, that is, having 200 residents and 200 workers is still
going to cause a problem.
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