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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | Re: [gislist] Census Boundary Files Origin |
| Date: |
10/27/2003 10:35:01 AM |
| From: |
Robert Heitzman |
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>I am not sure what "populated places" are meant, because I don't see
>anything called that in Census products. The data sets Caliper puts
>together include census places, legal and statistical, as polygons, from
>Census sources, along with point locations of "populated places" from USGS
>sources, the GNIS I believe, a data base of geographic names. The boundary
>files Census distributes come from the detailed geographic data base used
>in the Census operations and tabulations, TIGER, as do the TIGER/Line
>Files. Places in that context mean CDPs (statistical areas) and
>incorporated places (legal areas).
I stand corrected, I mixed terms from the two sources.
>
>Incorporated places and other legal areas come from the Boundary and
>Annexation Survey returned by local officials as the boundaries in effect
>Jan. 1 of the census year. The legal limits do not have to follow any
>visible feature, and are always made census block boundaries. CDPs are
>defined before the census in cooperation with local officials, often
>planning boards, and have to follow visible features, with a few exceptions
>such as short extensions of streets into RR or river features, and
>point-to-point lines between physical features. They are defined to
>represent what are locally regarded as "places" but are not legally
>incorporated. The CDP boundaries mostly follow the kind of feature that
>would be held as a block boundary in any case, and as tabulation areas for
>the census, have to be made census block boundaries because census blocks
>have to add up to any area that is to be tabulated.
>
This is a good theory but in practice the local jusrisdication boundary
files and the CDP areas available as GIS layers rarely line up 100%. Often
close. A lot depends on the coorperation and skill of the local Census
representative (not Census employees). Too little time and effort is
expended by the local reps IMO.
Another source of error may be the the local jusrisdictions publish
inaccurate boundary layers.
Another is the relatively slow change rate of TIGER data. Temporal errors if
you will.
Whatever the source of the error the overall point is that the CDP layer
should not be depended upon too greatly to truly represent the local
jusrisdication boundaries.
As more an more data is managed in GIS the better the CDP will become.
Perhaps the TIGER/MAF Enhancement Program will also have an impact. At least
make it easier for local agencies to add to or edit existing data.
Do you have any information on the status of the TIGER/MAF Enhancement
Program?
When might we see the first changes related to this project?
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