Curtis Price 20031124 Version 1 map http://water.usgs.gov/lookup/getspatial?uspopd90x10g This data set represents 1990 population density by block group as a 100-m grid using data from the 1990 Census of Population and Housing (Public Law 94-171 redistricting data). Grid cell values represent population density in people per square kilometer multiplied by 10 so that the data could be stored as integer. This is one of the ancillary GIS data layers developed to characterize USGS National Water-Quality Assessment (NAWQA), URL:http://water.usgs.gov/nawqa/, sampling sites for national synthesis of water-quality data. The ArcInfo Workstation grid is stored in the uspopd90x10g.tgz file (gzipped tar file). The uncompressed file size of uspopd90x10g.tar is about 59MB. Ways to extract the grid from the .tgz archive file include TARARC, Winzip, UnStuffIt, or the following GNU utilities for WIN32: >gunzip uspopd90x10g.tgz >tar xvof uspopd90x10g.tar The grid "uspopd90x10g" will be in a subdirectory called arctar00000. The data set is provided in 4 tiles in gzipped ASCII format--one for each quadrant of the country (NW,NE,SW,SE)--in addition to the native ArcInfo Workstation grid format. The ASCII files are provided as a nonproprietary format in case the user's software cannot access the data in ArcInfo Workstation grid format. The text files store the gridded population data in 4 files because in text format, a single file would be larger than 2.1 gigabytes in size, which is a hard file size limit for most 32-bit operating systems. The ASCII files are gzipped as uspopd90x10nw.txt.gz, uspopd90x10ne.txt.gz, uspopd90x10se.txt.gz, and uspopd90x10sw.txt.gz. Uncompressed file sizes of the ASCII files are: >uspopd90x10nw.txt 840488514 bytes (northwest quadrant of U.S.) >uspopd90x10ne.txt 1426174844 bytes (northeast quadrant of U.S.) >uspopd90x10sw.txt 1405014188 bytes (southwest quadrant of U.S.) >uspopd90x10se.txt 1761277532 bytes (southeast quadrant of U.S.) Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this Federal Geographic Data Committee (FGDC)-compliant file of metadata is intended to document the data set in nonproprietary form, as well as in ArcInfo format, this metadata file includes some ArcInfo-specific terminology. ArcInfo is part of the ArcGIS geographic information system software by ESRI, Redlands, California, <URL:http://www.esri.com>. Public Law (P.L.) 94-171 requires the Census Bureau to provide population data within a year following Census Day (April 1) to State governments so that the States can redraw their legislative districts. 1990 The data set is intended to represent conditions for the early 1990's. Complete No updates are planned unless errors or updates in the data occur. -127.975999 -65.254784 51.648905 22.768228 None Population Population density Demographic data P.L. 94-171 Census 1990 Census short form inlandWaters none Conterminous United States None. This data should not be used at scales smaller than 1:250,000. http://water.usgs.gov/GIS/browse/uspopd90x10g.gif 28KB GIF image showing overview of 1990 population density data GIF Microsoft Windows 2000 Version 5.1 (Build 2600) Service Pack 1; ARC 8.3 Spot checked with 100-m grid of 2000 population density. Visual checks. U.S. Bureau of the Census 1991 digital tabular data Washington, DC U.S. Bureau of the Census http://www.census.gov digital files on CDROM 1990 1990 Census of Population and Housing P.L. 94-171 Census of Population 1990 This source provided the tabular population and land area data used in calculating the population density for each block group. Population density in people per square kilometer was calculated from the tabular input data as pop1990 / arealand, where arealand is square kilometers. The population data are keyed to the block group boundaries using a block group identifier code. The source data was extracted from CD-ROMs containing Public Law 94-171 population and housing unit counts enumerated in the "100 percent processing" component of the 1990 Census. The "EXTRACT" program provided on the disks is a menu-driven program that allows the user to select the geographic level of detail and fields to be extracted from the data base. The data is organized by state. The counts were summarized by block group. U.S. Bureau of the Census 1991 digital data Washington, DC U.S. Census Bureau http://www.census.gov 100000 digital files on CDROM 1990 1990 1990 TIGER/Line This source provided the block group boundaries. The block group boundaries are keyed to the population density data using a block group identifier code. The block group boundaries were converted from polygon format to grid format. The TIGER/Line files are a digital database of geographic features, including census statistical boundaries, covering the entire United States. The TIGER files have no shorelines. Coastal areas have their boundaries extended approximately 3 miles into the ocean. Areas bounding the Great Lakes and other large inland waterbodies have their boundaries extended proportionally into the waterbody. The TIGER/Line files were converted into ArcInfo coverages by the Environmental Protection Agency's National Geographic Information System Program using ArcInfo programs developed with USGS. EPA provided USGS with county block group coverages in geographic coordinates. The county coverages for each state were joined into the state coverage, and each state coverage was projected to Albers. Curtis Price gridded the block group boundaries for each state at 100-m resolution and assigned each cell the integer value of population density times 10. The following ArcInfo Workstation GRID commands create the state grids: >&s ch [open bg.dat st -r] >&s file [read %ch% st] >&severity &error &routine bail >setcell 100 >relate add;p;uspop90.dat;info;bgi;bgi;linear;ro;; >&do &until %st% ne 0 >&s fn [entryname [before %file% .e00.gz]] >&s gn %fn%g >&if ^ [exists %gn% -grid] &then &do > &ty %fn% -- [date] [show &pt all] > &if ^ [exists %fn% -poly] &then &do > &sys gunzip -c %file% > %fn%.e00 > arc import cover %fn% %fn% > &s st [delete %fn%.e00 -file] > &end > setwindow %fn% snapg >/*POLYGRID converts data associated with polygon features to > grid cell format using the population density values > assigned to the polygons. >/*INT converts input floating-point values to integer > values on a cell-by-cell basis within the analysis window. >/*Adding .5 to the INT expression causes the integer numbers to be > rounded instead of truncated. > %gn% = int(polygrid(%fn%,p//pdens) * 10 + 0.5) >kill %fn% all >&end >&s file [read %ch% st] >&end >&s st [close %ch%] >&ty Done -- [show &pt all] >&watch &off >&return >&routine bail >&s st [close %ch%] >&ty Bailed -- [date] [show &pt all] >&return;&return The state grids were joined into a national grid. 20000128 Kerie Hitt re-projected the grid from NAD27 to NAD83 and renamed it. >projectgrid bgg27 bgg83 alb27toalb83.prj nearest nine 100 -2361500 259000 The resulting ArcInfo grid was compressed in size by copying it using the ArcInfo resample() function. This did not affect the grid cell values; it simply stored the data more efficiently. This step was necessary because of an ArcInfo bug: PROJECTGRID with the "nine" option does not effectively compress the output grid data set. >BGG83RES = resample (bgg83) >RENAME bgg83res uspopd90x10g 20030128 The merged national grid was too big to convert to an image for distribution. Instead, in case the user's software cannot access the data in ArcInfo Workstation grid format, the data was converted into 4 regional grid tiles, one for each quadrant of the country. The 4 regional grids then were converted to ASCII files containing rows of data corresponding to the grid cells. For example, >setwindow -2489750,1765250,-75250,3281750 >uspopd4 = uspopd00x10g >gridascii uspopd4 uspopd00x10se.txt Here are the boundaries of the 4 regional grids/ASCII files: >NORTHWEST >West_Bounding_Coordinate: -128.18 >East_Bounding_Coordinate: -98.18 >North_Bounding_Coordinate: 51.58 >South_Bounding_Coordinate: 36.82 > >NORTHEAST >West_Bounding_Coordinate: -98.74 >East_Bounding_Coordinate: -65.28 >North_Bounding_Coordinate: 51.60 >South_Bounding_Coordinate: 37.11 > >SOUTHWEST >West_Bounding_Coordinate: -123.34 >East_Bounding_Coordinate: -97.83 >North_Bounding_Coordinate: 39.96 >South_Bounding_Coordinate: 23.15 > >SOUTHEAST >West_Bounding_Coordinate: -98.30 >East_Bounding_Coordinate: -69.93 >North_Bounding_Coordinate: 39.98 >South_Bounding_Coordinate: 23.40 20030128 Raster Grid Cell 29184 46253 1 Albers Conical Equal Area 29.5 45.5 -96 23 0.00000 0.00000 coordinate pair 100.0 100.0 Meters North American Datum of 1983 GRS1980 6378137.000000 298.257222 The value of each 100-m grid cell is the population density in persons per square kilometer multiplied by 10 and rounded to the nearest integer to take advantage of ArcInfo integer grid compression. (A floating point grid would have exceeded the maximum file size allowed by 32-bit software applications.) The Census definition of urbanized area is 1000 persons per square mile or about 386 persons per square kilometer. That translates in this data set as an urban cutoff of about 3860 (386.0 persons per square kilometer multiplied by 10). Population density was calculated at the block group level (not at the grid cell level) originally as: >PPERKM2 = POP90 / AREALAND where AREALAND is square kilometers. The ArcInfo Workstation grid has no .VAT (value attribute table), but it does have a .STA (statistics file): > COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC > 1 MIN 8 15 F 3 > 9 MAX 8 15 F 3 > 17 MEAN 8 15 F 3 > 25 STDV 8 15 F 3 > >MIN is the minimum value in the grid (0). >MAX is the maximum value in the grid (1309231). >MEAN is the arithmetic mean of the values in the grid. >STDV is the standard deviation of the values in the grid. The ASCII files of data are provided in case the user's software cannot access the data in ArcInfo Workstation grid format. Each of the ASCII files consists of a 6-line header followed by population values in row-major order. Row 1 of the data is at the top of the grid, row 2 is just below row 1, and so forth. Each row of data ends with a carriage return. >NCOLS xxx (number of columns) >NROWS xxx (number of rows) >XLLCORNER xxx (x coordinate of lower left corner of grid) >YLLCORNER xxx (y coordinate of lower left corner of grid) >CELLSIZE 100 (100 x 100 meter cells) >NODATA_VALUE -9999 (cells with no data are coded as -9999) >row 1 (cell values for row 1) >row 2 (cell values for row 2) >... >row n (cell values for last row) The projection parameters are: >Projection ALBERS >Datum NAD83 >Zunits NO >Units METERS >Spheroid GRS1980 >Xshift 0.0000000000 >Yshift 0.0000000000 >Parameters > 29 30 0.000 /* 1st standard parallel > 45 30 0.000 /* 2nd standard parallel >-96 0 0.000 /* central meridian > 23 0 0.000 /* latitude of projection's origin >0.00000 /* false easting (meters) >0.00000 /* false northing (meters) Census Bureau U.S. Geological Survey Ask USGS - Water Webserver Team mailing

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Reston VA 20192 1-888-275-8747 (1-888-ASK-USGS) http://answers.usgs.gov/cgi-bin/gsanswers?pemail=h2oteam&subject=GIS+Dataset+uspopd90x10g Although this data set has been used by the U.S. Geological Survey, U.S. Department of the Interior, no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data and related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of this data, software, or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Grid Full coverage zipped 1 http://water.usgs.gov/GIS/dsdl/uspopd90x10g.tgz Other Text file zipped 1 http://water.usgs.gov/GIS/dsdl/uspopd90x10ne.txt.gz Other Text file zipped 1 http://water.usgs.gov/GIS/dsdl/uspopd90x10nw.txt.gz Other Text file zipped 1 http://water.usgs.gov/GIS/dsdl/uspopd90x10se.txt.gz Other Text file zipped 1 http://water.usgs.gov/GIS/dsdl/uspopd90x10sw.txt.gz None. This dataset is provided by USGS as a public service. 20041108 U.S. Geological Survey Ask USGS -- Water Webserver Team mailing

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Reston VA 20192 1-888-275-8747 (1-888-ASK-USGS) http://answers.usgs.gov/cgi-bin/gsanswers?pemail=h2oteam&subject=GIS+Dataset+uspopd90x10g FGDC Content Standards for Digital Geospatial Metadata FGDC-STD-001-1998