Price, Curtis Clawges, Rick 1999 1.0 map Open-File Report 99-78 Reston, VA U.S. Geological Survey http://water.usgs.gov/lookup/getspatial?ofr99-78_popdeng Grid of population density in the conterminous United States at a resolution of one kilometer. The grid was converted from an ASCII file obtained from the Consortium for International Earth Science Information Network (CIESIN). Large scale representation of population distribution in the conterminous United States. This data set was converted for use in the analysis of ground-water quality data on volatile organic compounds (VOCs) by the U.S. Geological Survey (USGS) National Water-Quality Assessment Program (NAWQA) VOC National Synthesis Team. PROCEDURES USED The data from which the population density grid was created was retrieved in ASCII format from data released by the Consortium for International Earth Science Information Network (CIESIN) (1995) and a FORTRAN program was used to convert it into a format that could be read into an ARC/INFO grid data set. The data was then projected from its original projection to an Albers projection using nearest-neighbor resampling. Detailed processing steps are included in this metadata file. The following documentation file also was released by CIESIN and is included here. > > >******************** BEGIN CIESIN README FILE ******************** > > The Socioeconomic Data and Applications Center (SEDAC) > > INTEGRATED DATASETS FOR THE USA > June 27 1995 > >--------------------------------------------------------- GENERAL The primary mission of The Socioeconomic Data and Applications Center (SEDAC), at the Consortium for International Earth Science Information Network (CIESIN), is to develop new policy oriented applications and information products that synthesize earth science and socioeconomic data. The SEDAC policy applications development effort is the primary means by which the Earth Observing System Data and Information System (EOSDIS) program helps to ensure that the scientific investment embodied in NASA's Mission to Planet Earth (MTPE) program leads to tangible benefits. Within this framework, the "Population, Land Use and Emissions" Task (PLUE) embarked on integrating data from different sources. Specifically, data from the US decennial census (1990) and recent satelite data were integrated. In the initial attempt, the focus is on transforming census vector based data to satelite pixel based data. >From the US census data Total Persons and Total Housing Unit Structures were the selected data items (from the blockgroup geography) to be merged with the Land Cover Characteristics database (square kilometer resolution) for the conterminous United States from the EROS Data Center. This land cover was derived from Advanced Very High Resolution Radiometer (AVHRR) 1990 multitemporal satelite data. LOCATION The US census blockgroup boundary information are present on a publicly accessible FTP archive: The Archive of Census Related Products. To access this Archive connect to > ftp ftp.ciesin.org <160.39.8.201> > user <log in as anonymous or ftp> > password <enter email address> > cd /pub/census Please read the file "archive.ann" and "archive2.ann" for a detailed description of this Archive which contains 11,000+ densely compressed boundary and demographic data files. The census blockgroup boundary files are located, by state, in /pub/census/usa/tiger. The Archive may also be reached via WWW at the URL http://www.ciesin.org/datasets/us-demog/us-demog-home.html The integrated data products are posted as generic compressed ascii files in the location in ftp://ftp.ciesin.org/pub/census/usa/grid The data files, their structure and creation, are described in further detail below. A series of graphic (GIF) files provide for a quick glance at the data products. In the near future, this information will be accessible via The Interactive System for Analysis Services (ISAS), a suite of query engines for WWW browsers. LAYOUT For each state, US census data and EROS Land Cover data have been integrated, meaning both datasets are reported at the square kilometer resolution for the conterminous USA. Support files include: > gridlgd.txt legend & variable/file descriptions > griddoc.txt [this file] > gridbox.txt bounding boxes for the states > gridcomb.sas file for data processing and image creation CREATION The integrated data were created using in-house developed algorithms written in C. A proportional allocation algorithm was applied. The individual steps of data processing are described next. a) The census blockgroups, derived from the US Bureau of the Census Topologically Integrated Geographic Encoding and Referencing database (TIGER/Line 1992), were first projected from their latitude-longitude source to the projection used in the Land Cover Charateristics database. This coordinate system is the oblique Lamberts Azimuthal Equal Area LAZEA) projection with an origin of -100 longitude and +45 latitude. The exact equations applied to tranform TIGER92 to this projection were: >X=Rkcos(lat)sin(long-long_origin) >Y=Rk[cos(lat_origin)sin(lat)-sin(lat_origin)cos(lat)cos(long-long_origin)] > >k={2/[1+sin(lat_origin)sin(lat)+ > cos(lat_origin)cos(lat)cos(long-long_origin)]}**1/2 R is radius of sphere (by default 6,370,997 meters) [from: Map Projections-A Working Manual by John P. Snyder, USGS 1987]. b) Once the boundaries are in LAZEA format, the selected data items from the census were merged into these files and submitted to a suite of programs. c) Proportional allocation. By state, each census blockgroup's bounding box is first determined in the LAZEA X-Y system. Next the area of overlap for each pixel (km2 grid) is determined. The sum of all overlapping areas is assigned as the total area of the polygon. Next, the data items, typically count type data (such as number of persons or buildings), are distributed across the intersecting grids based on the fraction of grid-overlapping-area over total-polygon-area. These steps are repeated for all polygons within each state and the values are accumulated in memory for each grid. (A check calculation is performed by adding all grid values for the polygon in question and verifying that the actual value does sum to the original total). In a final step, the accumulated total within each LAZEA X-Y grid are divided by the area of the grid itself to arrive at density measures (in our example, each grid is 1 kilometer by 1 kilometer, but this value may be changed). d) To make the data available in a generic way, the saved binary output files, one for each state, are accessed and the data dumped out in a generic image format. The structure of these files (the ??_int.zip files in ftp://ftp.ciesin.org/pub/census/usa/grid/pall) is as follows: > >2781 3475 1862 2569 xmin xmax ymin ymax >1.000000 1.000000 xsize ysize >0.000000 0.000000 0 pdkm hdkm lckm >0.000000 0.000000 0 pdkm hdkm lckm >1.105958 4.150659 91 pdkm hdkm lckm >0.736277 3.411086 136 pdkm hdkm lckm >... ... Records are shown for each grid inside the state's bounding box. The size of the image (bounding box) is determined by the points (xmin,ymin) for lower left and (xmax,ymax) for top right. The table size is rows=ymax-ymin by cols=xmax-xmin. The grid size is, in kilometers, reported on record 2. The sequence of the records reported from line 3 till end of file begin at (xmin,ymax) on row=1, col=1. Sequentially, all grid values are reported for row=1 until the end of row=1 is encountered (cols) before the row iterates and reporting starts at (row=2,col=1). These ascii files are then zipped with a CR-LF added to the end of each record (unix users use the unzip -a option replacng CR-LF with a LF). See the file "gridcomb.sas" for more detail. The file "gridbox.txt" summarizes all the bounding boxes for all states. e) When accessing multiple states, boundary conditions need to be corrected. For example, the state boundary line between two states could split a single grid. So the grid in question will get data allocated to it by both states . When splicing multiple states together these duplicate records need to be collapsed into one record. For the users this has been done for regions of the US (See the directory /pub/census/usa/grid/pall/us). The abbreviations used are: > Regional Area States > ------------------------ -------------------------- > NE NorthEast me nh vt ma ct ri ny pa nj > SA South Atlantic dc de md wv va nc sc ga fl > ESA East South Atlantic ky tn al ms > WSA West South Atlantic ar la ok tx > ENC East North Central mi wi il in oh > WNC West North Central mn ia mo nd sd ne ks > NWM North West Mountain mt wy id > SWM South West Mountain ut az co nm > PAC Pacific wa or ca nv From these files a USgrid.asc file will be put together for the whole US. More information on this file and a program to extract, based on any 2 points defining a rectangle, will be added into this file soon. These <REGION>grid.asc files have yet another file structure simplifying spatial retrievals based LAZEA X-Y. The layout looks like: >3556 1559 42.638058 16.016323 47 lazea-X lazea-Y pdkm hdkm lckm >3557 1559 5.12569 1.939586 47 lazea-X lazea-Y pdkm hdkm lckm >3336 1558 1.402889 0.5097 52 lazea-X lazea-Y pdkm hdkm lckm >... The file "gridbox.txt" can be used in conjunctions with these X,Y coordinates for spatial referencing. The "USgrid.asc" file created solves the boundary problems between regions. Consult the file "us/us-dist.txt" for simple stats on these files. PROBLEMS These files currently contain two problems which have been identified. Future releases will correct for these errors or approach the problem differently. In addition, in the future we will add more census and land cover varibales as well as emissions data. 1. Water areas receiving data in allocation program. First, this is explained by those grids on the shorelines. Part of the grid is water, part of the grid is land. The proportional allocation algorithm thus allocates census data to the grids for which there is partial water. The definition of the grid being water or land should be incorporated into the algorithm to fix this. The other problem in this area is those census blockgroups who consists of a large portion of water area and a tiny land area with significant population (see the Saginaw Bay area of Lake Huron). To avoid this problem, census blocks should be used which are either land or water, not a mixture of the two. 2. An oddity was discovered when examining the District of Columbia. In this area certain pixels receive data values that absolutely have no coverage with any of the polygons in the census blockgroup layer. We are currently investigating this problem and its effect on the integrated data layers. 3. A peculiarity. Certain areas of the census blockgroup coverage are missing because we were unable to "chain" the particular polygon. In other instances, large geographic areas might not contain persons in it. In both cases the density values assinged to the grid are 0. When integrating with the Land Cover grids, the with 0 density were missed when integrating the grid data. There does exist a Land Cover Characterization Code for these grids and their density values are zero. A peculiarity we did not catch in time when processing. 4. One LCKM values in the Northwest was assigned a nonsense value over the maximum possible of 159. Please delete this value. NOTE: Please note that the term "land use" is used loosely. Land cover is a better definition. The housing unit structures density is the only measure of urban activity in these data so far. Similarly, emissions data is at the current time lacking from the design. >--------------------------------------------------------------------------- Email comments/ideas/suggestions and bug reports to ciesin.info@ciesin.org Phone them in at: 517.797.2727 >********************* END CIESIN README FILE ********************* > > REVIEWS APPLIED TO DATA This electronic report was subjected to the same review standard that applies to all U.S. Geological Survey reports. Reviewers were asked to check the topological consistency, tolerances, attribute frequencies and statistics, projection, and geographic extent. The reviewers checked the metadata and a_readme.1st files for completeness and accuracy. REFERENCES Consortium for International Earth Science Information Network (CIESIN), 1995, Socioeconomic Data and Applications Center (SEDAC), Archive of Census Related Products: CIESIN/SEDAC, accessed July 21, 1998 at URL http://sedac.ciesin.org/plue/cenguide.html Environmental Systems Research Institute, Inc. (ESRI), 1997, ARC/INFO 7.1.1 Help, Redlands, Calif., [on-line documentation]. NOTES 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 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. Although this Federal Geographic Data Committee-compliant metadata file is intended to document the data set in nonproprietary form, as well as in ARC/INFO format, this metadata file may include some ARC/INFO-specific terminology. 1990 The data is described by CIESIN in their online documentation as derived from 1990 Census block-group level data. Complete None planned. -129.49760931 -64.43380054 48.63644682 21.80790306 None census population density inlandWaters None Conterminous 48 United States None None Curtis V. Price U.S. Geological Survey Physical Scientist mailing address

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Rapid City South Dakota 57702 United States of America 1-888-275-8747 (605) 355-4523 cprice@usgs.gov none Compilation of the data sets was supported by the National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey. The objectives of the NAWQA Program are to: (1) describe current water-quality conditions for a large part of the Nation's freshwater streams, rivers, and aquifers, (2) describe how water quality is changing over time, and (3) improve the understanding of the primary natural and anthropogenic factors that affect water-quality conditions. National analysis of data, based on aggregation of comparable information obtained from across the United States, is a major component of the NAWQA Program. These data sets were created in support of NAWQA national data analysis activities. Public Unclassified None Operating System: UNIX, ARC/INFO version 7.1.1 Not applicable No changes were made (except for integer truncation) of the persons per square mile grid and the reprojection to Albers coordinates. Grid cell size is one kilometer; accuracy of edges (coastlines, etc.) not tested. Unknown Consortium for International Earth Science Information Network 19950627 map NA NA NA Information available online http://water.usgs.gov/lookup/getspatial?ofr99-78_popdeng 2000000 online 19900101 ground condition none Array of population density values. The data from which the population density grid was created was retrieved from URL ftp://ftp.ciesin.org/pub/census/grid/us The original data file was formatted like this: >16 1909 0.150968 0.145122 149 >16 1910 0.384075 0.369201 149 >16 1911 0.407049 0.391286 149 >(... 245 MB of data) The first three columns represent row, column, and population density. A FORTRAN program was used to reformat the file into an input format used by the ARC ASCIIGRID command. The cell size, corner coordinates, and projection came from the documentation of the data files as posted on the CIESIN ftp site. (This documentation file is included in this metadata file.) The ASCIIGRID file was formatted like this: >ncols 4587 >nrows 2889 >xllcorner -2050500 >yllcorner -2136500 >cellsize 1000 >NODATA_value -9 >4 5 3 5 3 4 5 5 3 3 3 2 2 1 1 1 1 ... (4587 values per row) (data continues for a total of 2889 rows) The ARC/INFO ASCIIGRID command was used to read this into a grid, and the PROJECT command then was used to project the grid from its original projection (Lambert Azimuthal) to the Albers projection. Nearest-neighbor resampling was done to preserve the population density values through the projection change. This processing was performed by David Wolock, U.S. Geological Survey, Lawrence, Kansas. 19950829 Raster Grid Cell 2898 4521 Albers Conical Equal Area 29.5 45.5 -96 23 0.00000 0.00000 coordinate pair 1055.359799626 1055.359799626 METERS North American Datum of 1927 Clarke 1866 6378206.4 294.98 There is a value attribute table associated with this data set, as well as a file containing statistics about the grid. > >POPDENG.VAT: > >COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME > 1 VALUE 4 10 B - > 5 COUNT 4 10 B - > >VALUE contains values of population density. > >COUNT is the number of grid cells with each particular VALUE. > > >POPDENG.STA: > >COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME > 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 minumum value. > >MAX is maximum value. > >MEAN is the arithmetic mean. > >STDV is the standard deviation. None 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://water.usgs.gov/user_feedback_form.html 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. Export Full coverage zipped 1 http://water.usgs.gov/GIS/dsdl/ofr99-78_popdenge.gz Other DEM Format zipped 1 http://water.usgs.gov/GIS/dsdl/ofr99-78_popdengd.gz Grid Full coverage zipped 1 http://water.usgs.gov/GIS/dsdl/ofr99-78_popdenga.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+ofr99-78_popdeng FGDC Content Standards for Digital Geospatial Metadata FGDC-STD-001-1998