Wrbblks coverage for LULC 2000
Population density and dwelling units per acre were mapped and computed with block level Census 2000 Tiger/ Line data and Census 2000 Summary File 1 tabular data.
Census 2000 Tiger/ Line data can be found at:
http://www.esri.com/data/download/census2000_tigerline/
Census 2000 Summary File 1 can be found at:
http://factfinder.census.gov/servlet/DatasetMainPageServlet?_program=DEC&_lang=en

The Census 2000 Tiger/ Line data shapefiles were processed into coverages using ESRI’s geodatabase format and projected to UTM Zone 10, NAD 27 with ArcINFO.
Two tables were used from Census 2000 Summary File 1: P1. Total Population and  P15. Households.

For each county, tabular data were joined to the spatial data using the STFID.  The county coverages were joined prior to clipping to the WRB boundary.  Polygons that would be clipped by the WRB boundary were flagged for spatial proration of population and households.

Fields from wrbblks used to compute population and household
origarea	original polygon area ( for unclipped polygons origarea = area)
pr_ratio	for polygons clipped by the WRB boundary (bndpoly = 1), pr_ratio = origarea / area
bndpoly 	identifies polygons clipped by the WRB boundary ( value = 1)
totpop		block population from 2000 census
pop_adj	for unclipped polygons (bndpoly = 0), pop_adj = totpop. 
for clipped polygons, pop_adj = totpop * pr_ratio.
tothshld	number of households from 2000 census
hshld_adj	for unclipped polygons (bndpoly = 0), hshld_adj = tothshld  
for clipped polygons, hshld_adj = tothshld * pr_ratio
popdens	persons per square mile, popdens = (pop_adj / area) * 0.0000003861006)
hhdens 		households per acre, hhdens = (hshld_adj) / area) * 0.0002471054) 
ercres		translates hhdens into the 4 residential density classes of the WRB legend:
			for ercres  = 1, hhdens <= 4
			for ercres  = 2, hhdens > 4 and hhdens <= 9
			for ercres  = 3, hhdens > 9 and hhdens <= 16
			for erc res = 4, hhdens > 16

For LULC2000, the grid wrbhdens2 was produced by gridding on the ercres field.