The glcf1deg.dat.gz file contains a subset of the 1 Degree Global Land Cover data set derived from AVHRR, available from the Global Land Cover Facility at the University of Maryland. The subset is for southern Africa. This README file contains information regarding: 1. Data format 2. Procedure used to create the southern Africa subset 3. Legend and data source ------------------------------------------------------------------- DATA FORMAT ------------------------------------------------------------------- The downloadable file, glcf1deg.dat.gz, is a UNIX compressed file The data file is in ASCII Grid format for ArcInfo. The file contains a single ASCII array with integer values. Data values range from 0 to 12. Coordinates listed below are in decimal degrees. Rows 40 Columns 55 UpLeftX 5 UpLeftY -35 LoRightX 60 LoRightY 5 cellsize 1 Projection geographic The ASCII file consists of header information containing a set of keywords, followed by cell values in row-major order. The file format is {NODATA_VALUE xxx} row 1 row 2 . . . row n where xxx is a number, and the keyword NODATA_VALUE is optional and defaults to -9999. Row 1 of the data is at the top of the grid, row 2 is just under row 1 and so on. The end of each row of data from the grid is terminated with a carriage return in the file. Although the nodata_value is set to -9999 in the header portion of the glcf1deg.dat file, that value does not actually occur in the data set. To import this file into ArcInfo use the following command at an ARC prompt: ASCIIGRID {INT | FLOAT} Arguments - the ASCII file to be converted. - the name of the grid to be created. {INT | FLOAT} - the data type of the output grid. INT - an integer grid will be created. FLOAT - a floating-point grid will be created. ------------------------------------------------------------------- PROCEDURE USED TO CREATE THE SOUTHERN AFRICA SUBSET ------------------------------------------------------------------- The original data set was imported into ArcInfo using the ASCIIGRID command. Using GRID ( a raster- or cell-based geoprocessing toolbox that is integrated with ArcInfo) the SETWINDOW command was used to define the subarea of interest. This subarea was defined by identifying the bounding coordinates as follows: x_min 5 y_min -35 x_max 60 y_max 5 The "snap_grid" option of the SETWINDOW command was used. This snaps the lower- left corner of the specified window to the lower-left corner of the nearest cell in the snap_grid and snaps the upper-right corner of the specified window to the upper-right corner of the nearest cell in the snap_grid. In this case the snap_grid is the original data grid. The purpose of this is to ensure the proper registration of the newly set analysis window. The command format used is as follows: SETWINDOW x_min y_min x_max y_max original_grid Once the window was set, creating the new grid was simply a matter of setting the new subset grid equal to the original grid. subset_grid = original_grid An ASCII array was created from the new subset grid using the GRID command GRIDASCII. file.dat = GRIDASCII(subset_grid) ------------------------------------------------------------------- LEGEND & ADDITIONAL SOURCES OF INFORMATION ------------------------------------------------------------------- The following legend is used in the original data set: 0 Water 1 Broadleaf evergreen forest 2 Coniferous evergreen forest and woodland 3 High latitude deciduous forest and woodland 4 Tundra 5 Mixed coniferous forest and woodland 6 Wooded grassland 7 Grassland 8 Bare ground 9 Shrubs and bare ground 10 Cultivated crops 11 Broadleaf deciduous forest and woodland 12 Data unavailable Although not all of these categories may be represented in the subset of the data, the original legend has been retained. The original data and documentation can be obtained from the Global Land Cover Facility at the University of Maryland: http://glcf.umiacs.umd.edu ------------------------------------------------------------------- ORIGINAL DATA SET CITATION ------------------------------------------------------------------- DeFries, R. S. and J. R. G. Townshend. 1994. 1 Degree Global Land Cover Data Set Derived from AVHRR. Global Land Cover Facility, University of Maryland Institute for Advanced Computer Studies, College Park, Maryland, U.S.A. Available on-line at http://glcf.umiacs.umd.edu. ------------------------------------------------------------------- SUBSET DATA SET CITATION ------------------------------------------------------------------- Southern Africa subset of DeFries, R. S. and J. R. G. Townshend. 1994. 1 Degree Global Land Cover Data Set Derived from AVHRR. Global Land Cover Facility, University of Maryland Institute for Advanced Computer Studies, College Park, Maryland, U.S.A. Available on-line at ftp://www-eosdis.ornl.gov/data/safari2k_regional/land_cover_data_1deg