<URL:http://water.usgs.gov/nawqa-only/gw.html>
This data set consists of area weighting factors for 1990 Census block groups for NAWQA LUS and SUS areas. The weighting factors can be used to calculate population and housing statistics for data compiled by block groups.
This is one of the ancillary GIS data layers developed to characterize NAWQA ground water studies for national synthesis of water-quality data.
The 1990 block group input layer did not include Alaska and Hawaii.
Sites that fell outside the extent of the block group data layer are coded as -9999.
The block group weighting factors were created by overlaying each study area with the Census block group boundaries. The weighting factors show all block groups (BG) comprising the ground water study area and what fraction of the ground water study area each BG covers. The weighting factors are used to compute statistics for population and housing variables. This avoids doing multiple overlays of the study area and block groups (i.e., avoids doing an overlay for each Census variable).
Here is an example of part of a block group weight table:
GW STUDY BGI AREAKM2 AREAF USBG90_KM2 USBG90_F
ucollusrc1d_trg 080519638001 0.1 0.072 584.3 0.000
ucollusrc1d_trg 080519638003 0.4 0.462 102.6 0.004
ucollusrc1d_trg 080519638004 0.0 0.058 32.5 0.001
ucollusrc1d_trg 080519638005 0.3 0.408 2.7 0.117
______ _____
0.9 1.00 (AREAF should add to 1.)
BGI is the block group identifier (12-digit number). Four BGIs
occur in this particular study area.
AREAKM2 is the square kilometers of each block group in the
study area.
AREAF is the fraction of the ground water study represented by each
block group. (AREAF = AREAKM2/total AREAKM2 for study area)
USBG90_KM2 is the total square kilometers of a BLOCK GROUP.
USBG90_F is the fraction of the block group represented in the study area.
(USBG90_F = AREAKM2 / USBG90_KM2)
The values of 1990 population density for each BLOCK GROUP (from CENSUS data) are:
BLOCK GROUP POP DENSITY 080519638001 0.527 080519638003 4.765 080519638004 4.843 080519638005 202.105The weighted average of population density for ucollusrc1d_trg is calculated as:
BG BG BG BG BG BG BG BG TOTAL OF ALL
AREAF * POPDENS AREAF * POPDENS AREAF * POPDENS AREAF POPDENS AREAF's
POPDENS = (.072 * .527) + (.462 * 4.765) + (.058 * 4.843) + (.408 * 202.105) / (.072 + .462 + .058 + .408)
Processing routines are from the NAWQA area characterization
toolbox.
with doughnuts without doughnuts cut out (correct) not cut out (incorrect) AREAID GRID AREA (M2) GRID AREA (M2) cnbrluscr1_bnd 7,044,202,800.000 7,392,941,100.000 cnbrluscr1_trg 5,706,866,700.000 6,766,256,700.000 connlusrc1_bnd 1,756,677,600.000 2,064,634,200.000 connlusrc1_trg 587,594,700.000 610,191,000.000 connsus2_bnd 6,848,918,100.000 7,617,282,300.000 nvbrlusrc1_trg 155,431,800.000 155,443,500.000 spltluscr2_trg 207,267,300.000 228,433,500.000
Also added studies that are resampled studies, but do not have the same boundaries in cycle 2 as were used in cycle 1:
albelusag1, nvbrsus2, trinsus3, sanjluscr1a, sanjlusor2a.
Also added willlusag3, which has the same boundaries as cycle 1 willlusag2.
The data set is referenced by SUCODE (NAWQA study unit/network code) and AREAID (ground water study boundary coverage). Two kinds of ground water network polygon coverages exist: 1) BND coverages, which represent the entire areal extent of the hydrogeologic unit defined for study, and 2) TRG coverages, which delineate the targeted land use within the BND.
The data set is organized by AREAID. Missing data is indicated by -9999. An example of using the weighting factors to calculate average POPDENS for a ground water study area is shown under Process_Step.
Fields in the block group weighting table are:
SUID NAWQA study unit SUCODE NAWQA study unit/network code AREAID Ground water boundary coverage USBG90G Numeric representation of block group id (BGI) from 30m block group grid AREAG Flag indicating area is within a ground water study area (= 1) AREAKM2 Square kilometers of block group in the study area AREAF Fraction of the study area represented by the BLOCK GROUP USBG90_KM2 Total area of block group USBG90_F Fraction of block group in the study area (AREAKM2/USBG90_KM2) BGI Block group identifier
kjhitt@usgs.gov
kjhitt@usgs.gov