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A Publication Featuring The Information Services Technology of Maine State Government
|Volume V, Issue 11||November 2002|
By Kate King
Maines Census 2000 geography has been made available to local and global GIS communities through the Internet. Working in conjunction with the Maine State Planning Office (MESPO) Census Information Officer, the Maine Office of Geographic Information Systems (MEGIS) has developed three GIS datasets depicting different levels of Census geography in Maine. These are BLKS00, MCDCCD00 and VTD00 are published in the MEGIS Internet Data Catalog at http://musashi.ogis.state.me.us/catalog/catalog.asp. Each dataset is fully described by metadata in FGDC (Federal Geographic Data Committee) format which makes them also accessible to National Spatial Data Infrastructure (NSDI) clearinghouse nodes.
The use of Census data is simplified by an understanding of the spatial relationships between the different levels of Census geography. GIS is "the" tool for viewing these relationships and GIS simplifies the task of relating Census geographic units with statistical data tabulated by the Census Bureau. The smallest geographic unit for which the Census Bureau tabulates data is a Census Block. Geographic units, whose boundaries are delineated by the U.S. Census Bureau for statistical purposes within each Maine County include, nesting in order of size from smallest to largest, BLOCKS, BLOCK GROUPS, COUNTY SUBDIVISIONS, TRACTS. There are other Census geographies that represent specific groupings of BLOCKS within counties, some of these are CENSUS DESIGNATED PLACES, VOTING DISTRICTS, ZIP CODE TABULATION AREAS, and URBAN AREAS.
Because a Census Block is the smallest geographic unit for which the Census Bureau tabulates data, all other geographies, cross tabulated in the dataset BLKS00, can be mapped from the MEGIS dataset BLKS00. These include Census TRACTS, BLOCK GROUPS, VOTING DISTRICTS, DESIGNATED PLACES and COUNTY SUBDIVISIONS, COUNTY and STATE. The unique-id for each Census Block statewide is an attribute in the dataset. This is STFIDBLK00 which has been used as a key for the creation of unique identifiers for the other Census geographic units represented in the coverage and the COUSUB number, the unique-id for Census County Subdivisions (CCDs) is also included. Mapping by the unique-ids for each geography in BLKS00 makes it easy to see their relationship. In addition, the datasets MCDCCD00 and VTD00 offer Census 2000 County Subdivisions and Census 2000 Voting Districts for Maine as single themes. All the datasets are attributed with population. VTD00 also contains Senate, House and County Commissioner District numbers. Datasets for ZIP CODE TABULATION AREAS and URBAN AREAS are not currently available, but will be published when data becomes available.
The unique-ids for each Census geographic unit can also be used to relate or join the datasets to extended Census data files, counts, tabulations, and reference tables. Two such tables MEGEO and SF1BLKS00, from the Bureau of Census, have been published at the MEGIS Data Catalog TABLES link. Likewise, Maine GIS tables that assist with the analysis of Census geographic areas in relation to Maine minor civil divisions will be published as they become available. Three tables already published, GEOMCDCCD, MEPOPS, and POPMAPS are examples of these. See the TABLES link for complete description, and documentation of these tables. Additional tables from the Census Bureau will be published as they become available.
MEGIS Census 2000 GIS datasets BLKS00, MCDCCD00, and VTD00 were provided on CD in iBook compatible shapefiles to educators who participated in "Hands on Book" work sessions hosted by MEGIS at the October Maine GIS Users Conference at Orono, Maine. If you would like to learn more about Census 2000 data products, you can find an excellent brochure on Census 2000 data products "Introduction to Census 2000 Data Products" at http://www.census.gov/prod/2001pubs/mso-01icdp.pdf. The brochure maps out Census geography and related data products clearly, and provides succinct answers to some of toughest first questions about Census data. And heres a good link on Census history http://www.census.gov/prod/2000pubs/cff-4.pdf.
A graduate of the University of Maine Farmington in Interdisciplinary Geography and Geology, Kate King has worked as a GIS Coordinator for the Maine Office of GIS since 1996. Kate can be reached via email at firstname.lastname@example.org.
MEGIS Data Catalog http://apollo.ogis.state.me.us/catalog/catalog.asp
There is often no direct 1:1 relationship between minor civil division boundaries and Census geographic units. The rural character of Maine, and especially northern Maine, requires the Census Bureau to report counts and tabulations over larger areas for statistical reasons and the Bureau of Census redefines these areas as population shifts. Maine is one of twenty-one states where organized minor civil divisions do not exist statewide or where population is insufficient in some areas for reporting subcounty statistics. The Maine GIS dataset MCDCCD00 represents the closest correlation between Census geographic units and minor civil division boundaries. All other Census geographies represent areas either larger or smaller than town or township boundaries and often cross boundaries. In most cases additional analysis will be required to report Census counts and tabulations by town or township.
Census boundaries represent real world features like rivers, lakes, railroads, political boundaries, etc., but their primary purpose is for use in statistical analysis. As such, the features of the Census TIGER/Line Files, from which the MEGIS datasets were derived, may not coincide with representations of these features drafted for other purposes or at other map scales.
Here's a list of the Census related tables to be found at the Maine Office of Geographic Information Systems (MEGIS) Data Catalog TABLES link and info on how they relate or join to the Census geography datasets that MEGIS has published this year.
RELATES/JOINS to MCDCCD by COUSUB:
mepops.zip (populations by CCD 1950 through 2000 CAUTION! The Bureau of the Census redefines CCDs as population shifts. The correlation of data in MEPOPS from earlier census periods to Census 2000 CCDs is not exact.)
popmaps.zip (analysis 2000/1990 numeric pop change, percent change, density 2000 and density change)
geomcdccd.zip (crosswalk table Maine geocodes to USCB COUSUB numbers)
RELATES/JOINS to BLKS00 by STFID:
megeo00.zip (redistricting data file, the source of MEGIS Census 2000 population attributes in BLKS00, MCDCCD00 and VTD00)
sf1blks00.zip (summary file 1, counts from all people and housing units on age, sex, race, Hispanic or Latino origin, household relationship, and whether the residence is owned or rented)