ARC/INFO Generate (ASCII) Metadata Cartographic Boundary Files Scale and Generalization This document provides metadata concerning the ARC/INFO Generate (ASCII) files on the Cartographic Boundary Files web site. The cartographic boundary files have been developed for various internal Census Bureau projects and have been made available here to the general public on an "as is" basis. The Census Bureau recommends that these ASCII files only be used when use of the other available file formats is not possible. The ASCII format is not inherently compatible with GIS software packages. Use of the files requires some preprocessing as appropriate for the particular user GIS software package. A thorough knowledge of geographic concepts and GIS applications is highly recommended when attempting to use these files. As ArcView Shapefiles are easily imported into many GIS packages, Shapefile is the recommended format over ASCII files. ASCII File Composition | ASCII File Format | ASCII File Coordinates ASCII File Composition An ASCII format boundary file consists of two files: a polygon coordinate file and a polygon attribute file. File names for 2000 polygon coordinate files incorporate an abbreviation for boundary type, a 2-digit State FIPS code, a "d" to indicate Decennial Census activity (when applicable), a 2-digit vintage number (last two digits of the vintage year), and a .dat file extension. Older polygon coordinate files also include a "p" after the vintage. 2000 polygon attribute files include an "a" after the vintage number (the "a" follows the "p" for older files. For Congressional District boundary files the number of the congress replaces the two digit vintage number. For more information on filenaming conventions for the cartographic boundary files see the Filenaming Conventions page. Examples of ASCII filenaming convention: an02_d00.dat 2000 Alaska Native Regional Corporations polygon coordinate file for Alaska cd31_107a.dat 107th Congressional District polygon attribute file for Nebraska co10_d90_pa.dat 1990 County polygon attribute file for Delaware Return to Top | ASCII File Composition | ASCII File Format | ASCII File Coordinates ASCII File Format Polygon coordinate files follow the format: ID LON1 LAT1   LON2 LAT2   ... ...   LONx LATx END     ID LON1 LAT1   LON2 LAT2   ... ...   LONx LATx END     END       where ID = a unique polygon identification number, LON/LAT = a longitude/latitude coordinate internal to the polygon, and LONn/LATx = a sequence of longitude/latitude coordinate pairs defining the polygon vertices, with matching first and last vertices. An END statement indicates the termination of each polygon, and a final END statement indicates the termination of the polygon file. Islands or exclusions within a polygon are flagged with an ID number of -99999. The outer cycle of a complex polygon is listed first, followed by any islands. For example: 31 LON1 LAT1   LON2 LAT2   ... ...   LONx LATx END     32 LON1 LAT1   LON2 LAT2   ... ...   LONx LATx END     -99999 LON1 LAT1   LON2 LAT2   ... ...   LONx LATx END     END       See ASCII File Coordinates for greater detail on longitude/latitude values.   2000 polygon attribute files follow the format: ID FIPS CODE(S) NAME LSAD LSAD TRANSLATION Older polygon attribute files vary in compostion, but always include an ID value and a geocode for each entry in the polygon attribute file. Some files additionally include name information. In the future ASCII files may be updated to more closely match the structure and integrity of the 2000 ASCII files. Return to Top | ASCII File Composition | ASCII File Format | ASCII File Coordinates ASCII File Coordinates Longitude and latitude coordinates are expressed in decimal degrees, with longitude values ranging from -180 to 180 and latitude values ranging from -90 to 90. The intersection of the Greenwich Prime Meridian and the Equator is taken as the origin. A coordinate pair is signed according to the quadrant in which it falls relative to the origin. Signs of coordinate pairs by quadrant are: Northeast + Lon + Lat Northwest - Lon + Lat Southeast + Lon - Lat Southwest - Lon - Lat Coordinate values for 1998 and newer files are based on the GRS1980 spheroid, also referred to as the North American Datum, 1983 (NAD83). Coordinate values for files previous to 1998 are based on Clarke's spheroid of 1866, also referred to as the North American Datum, 1927 (NAD27). Return to Top | ASCII File Composition | ASCII File Format | ASCII File Coordinates

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Page Last Modified: April 19, 2005