GRIDDED 1 KM POPULATION ESTIMATES FOR THE CONTERMINUOUS U.S., 1930-2000

The files are in flat ASCII format with the following information by column:

1.  State NCDC Number 
2.  State Postal Abbreviation
3.  County Name
4.  County FIPS Code
5.  Longitude (decimal degrees)
6.  Latitude (decimal degrees)
7.  2000 population for grid point
8.  1990 population
...and so forth back to 1930.

About this data set:

Population values at a 1 km2 grid cell resolution were prepared for the
conterminous United States (CONUS) for 1930-2000 using two U.S. Census 
Bureau data sets:  The 2000 U.S. Census Bureau 1 km2 population density 
grid for CONUS (National Geophysical Data Center/NESDIS/NOAA, 2002) and 
tabular U.S. Census county data (U.S. Census Bureau 2002).  These data 
sets were merged in two steps.  First, the 1 km2 2000 gridded population 
density dataset for CONUS was merged with a 1 km2 gridded data set that 
defined the spatial extent of all counties.  This combined information 
was then used to estimate the spatial distribution of population within 
each county for each decade.  Weights for each grid cell, summing to 1.0 
for each county, were computed.  Then these weights were multiplied by 
the county total for each decade.  Finally, values were adjusted for 
rounding so that the sum of each county's grid cells precisely matched 
the published census values. 

National Geophysical Data Center/NESDIS/NOAA, 2002:  Land Use Change 
Project Data: 2000 U.S. Census Population Grids 
(http://dmsp.ngdc.noaa.gov/html/download.html).

U.S. Census Bureau, 2002:  Population of States and Counties of the 
United States:  1790-2000, Washington, D.C., 226 pp.