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We are pleased to announce the availability of Geocorr, Geographic
Correspondence Engine.
The MABLE / Geocorr geographic correspondence engine generates files
and/or reports showing relationships between a wide variety of geographic
coverages for the United States. This application allows you to specify
the geographic scope of the correspondence files ( typically one or more
complete states, but with the ability to specify counties, cities or
metropolitan areas within states) and the geographic coverages to be
correlated. Coverages available for correlation include all geographic
units reported in the 1990 census Summary Tape Files, and several special
"extension coverages", including congressional districts for the 103rd
Congress and PUMAs used in the 1990 Pulic Use Microdata Samples (PUMS).
Population, housing unit counts or land area can be used as the weighting
variable to determine the proportion of correlation between units of the
source geographic area codes and units of the target geographic area
codes, or geocodes.
MABLE - The Underlying Database
MABLE is an acronym that stands for Master Area Block Level Equivalency
file. This is the database that is used by the Geocorr engine to create
correlation lists. "Block" here refers to 1990 census blocks, the
smallest geographic units used in the 1990 census. It was chosen as the
base unit for the application because the Bureau of the Census uses these
blocks as the "atomic unit" for all other census based geographies. The
MABLE database is a collection of 51 state-level datasets containing a
total of nearly seven million block entries, each of which contains
geographic code information to locate the block within all higher levels
of the census geographic hierarchy.
Geocorr- Building Correlation Lists
Geocorr identifies the blocks that are within the scope of the area of
analysis by units of source geocode and reaggregates them into the units
of the target geocode. "Allocation" factors, the overlap or intersection
between source and target geographies as determined by the chosen
weighting factor, are calculated and reported. For example:
County Tract Zip Population AFact
29510 1101.00 63109 1250 .500
29510 1101.00 63110 625 .250
29510 1101.00 63111 625 .250
This example shows that the scope of analysis is a single census tract,
1101.00, in a single county (the city of St. Louis, MO). The source
geocode is the tract. The target geocode is the five-digit zip code. The
sum of the population for each zip code within the tract equals the total
population of the tract. The sum of the allocation factor (AFact) values
is always 1.0.
Access
The Geocorr engine is available through the following two URLs:
http://plue.sedac.ciesin.org/plue/geocorr
http://oseda.missouri.edu/plue/geocorr
The "sedac" site is the primary mirror, but both sites offer the same
functionality at all times.
This service is provided by the Socioeconomic Data and Applications Center
(SEDAC). The Consortium for International Earth Science Information
Network (CIESIN) has been designated by the National Aeronautics and Space
Administration (NASA) to create and operate SEDAC, one of the data centers
in the Earth Observing System Data and Information System (EOSDIS).
SEDAC's mission is to develop and deliver information products and
services that integrate social and natural science data in ways useful for
decision making.
For additional information about MABLE / Geocorr, SEDAC, or CIESIN,
contact User Services at [log in to unmask] or call (517)797-2727
between 8 a.m. and 5 p.m. eastern time, Monday through Friday.
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