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U.S. Population Grids (Summary File 3): Alabama, Louisiana, and Mississippi, alpha (2000)

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DATA DESCRIPTION

U.S. Population Grids (Summary File 3), 2000: Alabama, Louisiana, and Mississippi (alpha version)

This archive contains an ArcInfo workspace with grids of demographic data from the year 2000 census. The grids cover the states Alabama, Louisiana, and Mississippi for the set of variables described below. The grids are stored in geographic coordinates with the following parameters:

Projection:     Geographic
Spheroid:    WGS84
Datum:        NAD83    
Units:        Decimal Degrees

The grids have a resolution of 30 arc-seconds (0.0083 decimal degrees), or approximately 1 square km.

The gridded variables are based on census block and census block group geography from Census 2000 TIGER/Line Files and census variables (income, poverty status, educational attainment, and housing variables) from Summary File 3. Census block group data are allocated to census blocks using variables from Summary File 1 (see below for more information).

For more details on these sources see:

Census 2000 TIGER Line Files: http://www.census.gov/geo/www/tiger/tigerua/ua_tgr2k.html

Summary File 1: http://www.census.gov/census2000/sumfile1.html

Summary File 3:  http://www.census.gov/census2000/sumfile3.html

The Summary File 3 variables are transformed from census block groups to census blocks using a proportional allocation based on an appropriate variable from Summary File 1. For Summary File 1 variables, the census block is smallest geographical unit for which data are reported. For Summary File 3 variables, the smallest reporting unit is census block group. To transform census block group data to census blocks, the proportion of the census block group's Summary File 1 variable in each census block is calculated.  This proportion is multiplied by the Summary File 3 variable to determine a value for each census block.

For instance, the Summary File 1 variable used for the educational attainment variable is the population age 25 and older.  If a census block contains 50% of the block group's population age 25 and older as reported in Summary File 1, that census block is allocated 50% of the census block group's population with an education attainment level of a high school degree or less, as reported in Summary File 3.  The Summary File 1 variable used to allocate each variable is described below.

Once the variables have been transformed to census blocks, they are transformed to a quadilateral grid using proportional allocation.  An explanation of proportional allocation is available in the What's a Grid? page from GPW v3.

VARIABLES

All variables are stored as counts (i.e., number of persons), one per grid. For the easy calculation of density grids, a land area grid is included. To create a density grid (per square kilometer), simply divide a count grid by the land area grid.  To create a percentage grid, divide a count grid by the count grid that represents the universe for that variable.  For example, to calculate the percentage of housing units without a vehicle, divide the number of occupied housing units without a vehicle by the total number of occupied housing units.

Certain variables, including population, number of households, and number of housing units are gridded in both the U.S. Population Grids (Summary File 1), 2000 and the U.S. Population Grids (Summary File 3), 2000.  The values for the two sets of grids will not be identical.  The U.S. Population Grids (Summary File 1), 2000 are based on data from the Census 2000 short form.  These data are collected for all households in the country. The U.S. Population Grids (Summary File 3), 2000 are based on the Census 2000 long form, which was completed by approximately one in six households.  The population totals in Summary Files 1 and 3 are not identical.  A full explanation of the differences is available at:

http://www.census.gov/census2000/sf3compnote.html

When calculating the percentage of the population with a given Summary File 3 variable, use the correct Summary File 3 variable as the denominator.  Using the Summary File 1 variable may result in values of more than 100%.

Variable descriptions by grid name:

Population
GCPOP300G    Population counts
GCP2500G    Population age 25 and older
GCPVP00G    Population for whom the poverty level is determined
GCHH300G     Number of households

Income
GCSEVP00G    Population living at less than 50% of the poverty level
GCPOV00G    Population living below the poverty level
GCLOWI00G    Population living at less than 200% of the poverty level
GCAHHI00G    Aggregate household income in 1999

Education
GCEDU00G    Population age 25 and older with a high school degree or less as their maximum level of educational attainment

Housing
GCHU300G    Housing units
GCOCC300G    Occupied housing units
GCHUNV00G    Occupied housing units without a vehicle
GCHA100G    Housing units built between 1990 and 2000
GCHA200G    Housing units built between 1970 and 1989
GCHA300G    Housing units built between 1950 and 1969
GCHA400G    Housing units built between before 1950

Area
GCAREA00G    Land area in square kilometers

The Summary File 1 variable used to allocate census block group data to census blocks is shown in the righthand column:

Population
GCPOP300G    Total population
GCP2500G    Population age 25 and older
GCPVP00G    Total population
GCHH300G     Number of households

Income
GCSEVP00G    Total population
GCPOV00G    Total population
GCLOWI00G    Total population
GCAHHI00G    Number of households

Education
GCEDU00G    Population age 25 and older

Housing
GCHU300G    Number of housing units
GCOCC300G    Occupied housing units
GCHUNV00G    Number of occupied housing units
GCHA100G    Number of housing units
GCHA200G    Number of housing units
GCHA300G    Number of housing units
GCHA400G    Number of housing units

For more details, see the spreadsheet included in the archive (SF3_Variable_documentation.xls).

ACKNOWLEDGEMENTS

This work, including access to the data and technical assistance, is provided by CIESIN, with funding from the National Aeronautics and Space Administration under Contract NAS5-03117 for the Continued Operation of the Socioeconomic Data and Applications Center (SEDAC).