FAO-UNESCO SOIL MAP OF THE WORLD FOR AFRICA; GRID VERSIONEntry ID: GNVd0035_104
Abstract: The Africa Soils database resident at UNEP/GRID-Geneva is derived from the Global Soils database digitized by the ESRI Corporation in Redlands, California (USA) from the 1974 FAO/Unesco Soil Map of the World at 1:5,000,000 scale. The legend of the Soil Map of the World comprises an estimated 5000 different mapping units, consisting of soil units or associations thereof, occurring within the limits ... of a map- pable physiographic unit (Africa alone in three map sheets has a total of 1509 map units). The number of soil unit classes which compose the FAO/ Unesco Soil Map of the World legend is 106. In the UNEP/GRID version, this has been increased to 129 to allow the identification of soils where insufficient information existed to specify the dominant soil unit.* In- stead, the dominant soil GROUP is identified (e.g., 'Acrisols' when the dominant Acrisols UNIT is not known). When a map unit is not homogene- ous, it is composed of a dominant soil and associated soils, with the latter covering at least 20 per cent of a given area. Important soils covering less than 20 per cent of a given area are added as inclusions.
The original FAO/Unesco Soil Map of the World, published in a total of 19 map sheets (including the legend), was in the Bipolar Conic Conformal Projection for the Western Hemisphere, and in the Miller Oblated Stereo- graphic Projection for the Eastern Hemisphere. In order to have a global digital data set that was consistent and uniform, the vector-based data files were first rasterized and then re-projected at GRID-Geneva into the Plate Carree or Simple Cylindrical Projection (a particular form of the Equirectangular). The original digitized polygon vertices in table coordinates were rasterized and georeferenced using the ELAS (NASA's Earth Resources Laboratory Applications Software) programs on a Perkin- Elmer 3241 minicomputer, with an output cell (pixel) size of 30 seconds latitude/longitude spatial resolution (approx. 925 meters at Equator), or 0.86 square kilometers/pixel. The resulting database was also gene- ralized (resampled) to two minutes latitude/longitude resolution (approx. 3.7 km. on a side), yielding an output cell size of 13.7 sq. km. This is the spatial resolution UNEP/GRID-Geneva normally recommends to most users, and indeed at which it most frequently distributes the data set.
The original FAO/Unesco Soil Map of the World included information on texture, slope and phase, but separate data layers depicting these variables have not been developed by UNEP/GRID.
The proper reference or original source document for this data set is as follows: "FAO/Unesco Soil Map of the World, 1:5000000, ten volumes, Unesco-Paris 1974."
There are two versions of the FAO/Unesco Soil Map of the World for Africa available from GRID-Geneva, at two minutes latitude/longitude spatial resolution, and also at 30 seconds latitude/longitude spatial resolution (the two-minute data file is more commonly distributed). The first consists of 2191 rows (lines, records) by 2161 columns (elements, pixels, samples), and the second has 8761 rows by 8641 columns. Both have an origin (upper-left or northwest corner) of 38 degrees/00 minutes/45 seconds North latitude and -20 degrees/ 01 minutes/15 seconds West longitude, and extend to -35 degrees/ 00 minutes/30 seconds South latitude and 52 degrees East longitude at their terminal point (lower-right or southeast corner).
* - There are 106 original Soil Units, and 27 ("Great") Soil Groups; of these, 23 were composed of various soil units and four had ONLY the Group name designations. Therefore, it was only necessary to add 23 new classes to the UNEP/GRID version legend, for 129 in total (106 + 23 = 129). There are three additional categories in the GRID legend for Rock, Salt and Water, or 132 classes altogether.
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Access Constraints Public
Role: TECHNICAL CONTACT
Email: Hy.Dao at unep.org
Head of Metadata & Socio-Economics Unit
Postal Code: 1219
Creation and Review Dates
Last DIF Revision Date: 2012-02-01