At Ed Christopher's suggestion I am posting this to the list server.
The following are some observations on the E-mail traffic I have been
observing with respect to the CTPP summarization issues that I have
raised with Ed at and since his sub-committee meeting at TRB last
January. I must note that more recent e-mail is now starting to mention
Phil Salopek in a recent e-mail says if you want Census geography
instead of TAZ you don't have to participate in the TAZ up
program....well at NYSDOT we want the statewide element of the CTPP
to be detailed to CDP or lower and all the urban area elements for our
use to be detailed to Census geography....tract and block group as the
lowest level in the urban area.
NYSDOT is interested in Census geography at the block group level
especially in urban areas. Since each of the MPOs will be responding
separately to the CTPP TAZ questionnaire, in addition to NYSDOT, then
MPOs will indicate their need for TAZs or census geography. This way
the MPOs can get what they want and the state can get what it needs.
The glitch is if Census or Phil Salopek says the state has to have it the
Frankly I don't see the problem....the CTPP is part of the STF3. As part
of STF3 it is summarized for CTPP parts A and 1 to the block / block
group level and everything above from the get go. All that is required is
the production of STF3 for the work place. County work flow is
produced very early on in Census processing prior to the CTPP. These
data are historically available on the REIS CD. So for the most part
Census provides CTPP part C or 3 at the county level outside of CTPP.
Clearly they have the routines in place to do it by specifying lower
geography with selected focus (such as state or metro area). So its not
just a CTPP processing software issue.
The real issue is getting Census to recognize several things:
1 Census geography should always be available as a summarization
level for all locations
2 If you are not an urbanized area 50,000+ then you likely do not have
an MPO, and you do not have TAZs even though you may be a small
3 TAZs are unique to "MPOs with models" and they don't define TAZs
them the same way
4 If you are not now an urban area now and eventually become one in
say 2002 then you are out of luck if TAZ is the only summarization level.
This may be especially painful when we move to the ACS.
5 If you need to add TAZs , combine or subdivide them later you can't
6 This is not just an MPO product
7 This is really a summarization level issue like congressional boundaries
8 The problem that Census really needs to address is how to aggregate
data up from lower geography for values such as mean and median;
where summarization is really not possible ( median income or median
travel time for example). Resolving this problem then enables Census or
the end user to create the data at the lowest possible geographic unit
and provide a summary level routine for computational values. All the
MPOs need then is a simple lookup table to relate TAZs to Census
geography and a routine to fix the computational values
9 From a purely economic product perspective Census geography
means you can sell the product to third parties and recover the cost.
TAZ is a summarization level unique to MPOs. There are lots of value
added resellers of STF3 data now in addition to Census. The CTPP
creates the workplace version of STF3 for a number of measures that
are important to not only transportation planners but also to anyone
interested in who, how and/or what arrives at work place locations.
10 Remember to make sure that the CTPP coding uses Census FIPS
codes and not Census Place codes that Caliper used in 1990, otherwise
it will not directly match common tiger based coverages.
11 The CTPP software that extracts the data table components from the
CD rom needs to be improved on the data extraction part. Often one
wants some range of Fips or town county, state codes for either the
residence , work place or JTW and for selected fields (e.g. total trips,
transit). As the 1990 CTPP software works you get all geography that
you can point to on the map, not bad on the statewide side except if you
want trips from selected origins outside the state. If you are using the
urban element then selection is much more difficult because of the level
of detail. In either case JTW from selected to selected geography is not
easily do-able except in a database product. Some accommodation on
the direct data selection side rather than through the visual graphical
user interface would be helpful. Something like "extract" the Census
routine for use with the Census STF CDs would be helpful. Otherwise
you really need a database product like SAS, Paradox, dBASE or
Access to get at the data the way you want.
12 What would really help would be Census creating STF3 for the
workplace and the present county work flow data for lower
13 Lastly it might be useful to note that at NYSDOT many of the
information requests I receive come from the economic development
interests. These requests reflect transportation or government concerns
for attracting businesses into NYS. They come from within our agency or
from our State Economic Development agency. These questions typically
ask about workers first and then where they live. NYS can't be that
different from the rest of the states that compete for the location of new
jobs. Many of these requests are for areas just outside of the urban
boundary. The fact that these type of informational questions are being
asked illustrates the value of detailed Census geography and
summarization levels beyond what has been provided for at the
metropolitan planning through TAZs.
As always I am available to discuss some of the more mechanical
technical aspects of using the CTPP data in non TAZ analyses with
anyone who wants to discuss why one size does not fit all.
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