30 Apr
1999
30 Apr
'99
2:11 p.m.
mike, i hope you don't mind but i felt this was an issue for the list
serve. the concept of a dual tabulation (tracts and tazs) within MPO
areas has come up at several different times. i believe that the current
thinking is that inside mpos the tabulation for worker data and the flow
data will be at the taz geography only. however, the table content is
still being developed so i believe this is an open issue. to me you
make a very valid point. at a tract or coarse level the flow data
becomes higher in quality but at a smaller area, like a taz, the
household demographics are needed and quite reliable.
it has also been my understanding that we are working towards a ctpp
product that has TAZs within mpo areas and whatever the states' want
outside the mpo areas. the only parameter would be that either zonal
system nest within counties and thus states. if the states can work
with their mpos to have their tazs nest within tracts, as chuck purvis
of san francisco's mpo is doing, then an equivalency file would take
care of the tract issue. the only difficulty there might be with
variables using medians but a good approximation could certainly be
calculated.
we have also talked about the possibility of developing a (for cost)
special tabulation for those who wish to get something above and beyond
the ctpp. right now i can't think of any examples except maybe some type
of 8-way cross tabulation no one else ever thought of.
mike i may not have given you any definitive answers but i would suggest
that you keep in mind the concept of having TAZs nest within other zonal
systems and the use of equivalency files for aggregation. maybe we can
get some creative folks to develop an "on the fly" buffering ability
that can, with the push of button, produce data summaries for whatever
zones we desire. coming out of 1990 we at cats in chicago were dabbling
with this idea but then conformity issues and a long range took us
over.
MIKE JAFFE wrote:
To: Ed Christopher
I have a question that I originally asked Tom Mank
about last December (but unfortunately didn't get an
answer), and I think its important for other MPO's to
know what the census is planning.
We're participating in the TAZ-Up program because
we want certain census data (including CTPP data)
tabulated at our TAZs. This is particularly helpful in the
development of our household sociodemographic
cross tabular data (e.g number of workers by
household size) that are inputs to our travel model.
On the other hand, CTPP at the Census Tract level is
useful for more aggregrate analysis, such as journey
to work patterns and mode choice, where the
statistical reliability at the census tract level is
preferred. Therefore, ideally we need the CTPP data
summarized for both TAZs and Census Tracts within
MPOs; outside MPOs, as Ed Arabas notes in his
email, census tracts are more appropriate.
Therefore, I need to know whether MPOs will get
Census data for both TAZs and Census Tracts within
their MPO boundaries. The 1990 CTPP came in two
geographic levels: the urban level CTPP and state
level CTPP. Will this be the format for 2000, and if so,
can the urban level have the MPO TAZs and the State
Level have census tracts, including census tracts
inside the MPO?
I look forward to your response.
Mike Jaffe
Senior Transporation Planner/Modeling
Salem Keizer Area Transportation Study (MPO in
Salem, Oregon)
Phone: 503-588-6177
email mjaffe(a)open.org