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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 11:25:01 AM |
| From: |
charles.e.dingman .. census.gov |
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CDP's do not represent jurisdictions that are incorporated, and are not
meant to follow other legally defined entities, so I am not following your
take on the correspondence or lack of it between CDP boundaries and other
local boundaries. The area may have changed between the time CDPs were
delineated and the census date, so that a CDP might not represent the full
extent of a community at the time of the census. The one CDP boundary
update that is and must be made just before the census is to trim CDPs to
align with corporate limits of adjoining legal places as of Jan. 1 of the
census year. Also, if you are looking at the cartographic boundary files,
they are all generalized to simplify their shapes, and reduce their size
and drawing time, so they no longer match exactly to similar files taken
from the TIGER/Line Files, which show every vertex or shape point we have
stored for the boundaries.
The features that are getting updated presently in the MAF/TIGER accuracy
improvement part of the enhancement are primarily roads and streets, with
some hydrography and a few local boundaries. To get the best data sources
and further partnerships, local/tribal government sources are being used
wherever possible. The results of early coordinate improvements for 20
counties were in the 2002 TIGER/Line Files and 107 more counties will show
up in the 2003 files.
CDP boundary updates are still on a decennial schedule, right now, although
census planners are looking at how they might be revised more frequently to
serve the ongoing American Community Survey, since it will provide updated
statistics every year. For the areas below 65,000 population, like most
CDPs and incorporated places, it will take 3 to 5 years to accumulate
enough of a sample for reliable estimates of population and housing
characteristics and the statistics will be rolling averages.
Another part of the enhancement program is redesigning the whole census
geographic support system, and one goal of that is to make the information
more easily shared and updated with our partners. Technology and standards
are both headed in the direction of interoperable systems that will make it
much easier to use one another's data without import/export
transformations, and we are actively working with Open GIS Consortium and
others to make that happen.
Charles Dingman, Geographer/301-763-1120
Rm 425, WP-1, Geography Division
US Census, 4700 Silver Hill Rd Stop 7400
Washington, DC 20233-7400
|---------+---------------------------->
| | "Robert Heitzman"|
| | <rheitzman@hotmai|
| | l.com> |
| | |
| | 10/27/2003 11:34 |
| | AM |
| | |
|---------+---------------------------->
>--------------------------------------------------------------------------------------------------------------------------|
| |
| To: charles.e.dingman@census.gov |
| cc: CWeaver@icfconsulting.com, gislist@lists.thinkburst.com |
| Subject: Re: [gislist] Census Boundary Files Origin |
>--------------------------------------------------------------------------------------------------------------------------|
>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
>
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