[CTPP] Size of TAZ (second try--this time includes the response!)

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 suppressed. 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.