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Global Map of Irrigation Areas (GMIA)
Latest version (5.0)
The latest version of the "Global Map of Irrigation Areas" is version 5, which can be downloaded from this page. The documentation of the map includes an explanation of the methodology, information per country, an assessment of the map quality, and references to the background and history of the irrigation mapping project.
The map shows the amount of area equipped for irrigation around the year 2005 in percentage of the total area on a raster with a resolution of 5 minutes. Additional map layers show the percentage of the area equipped for irrigation that was actually used for irrigation and the percentages of the area equipped for irrigation that was irrigated with groundwater, surface water or non-conventional sources of water. An explanation of the different terminology to indicate areas under irrigation is given in this glossary. Please note that information for the additional layers on area actually irrigated or on the water source for irrigation was derived from statistical survey data (e.g. census reports). Therefore all grid cells belonging to the same statistical unit will have the same value. Consequently, the accuracy at pixel level will be very limited, depending on the size of the statistical unit.
Users are requested to refer to the map as follows: "Stefan Siebert, Verena Henrich, Karen Frenken and Jacob Burke (2013). Global Map of Irrigation Areas version 5. Rheinische Friedrich-Wilhelms-University, Bonn, Germany / Food and Agriculture Organization of the United Nations, Rome, Italy".
The map layers are generated as a grids and distributed with the following characteristics:
|Number of columns:||4320
|Number of rows:||2160
|North Bounding Coordinate:||90 degrees
|East Bounding Coordinate:||180 degrees
|South Bounding Coordinate:||-90 degrees
|West Bounding Coordinate:||-180 degrees
|Cellsize:||5 minutes, 0.083333 decimal degrees
|NODATA values: ||Cells without irrigation are characterised by NODATA (-9), it does not mean that there was no data for these cells
For the GIS-users the map is distributed in two different formats: as zipped ASCII-grid that can be easily imported in most GIS-software that supports raster data or grids; and, to accommodate people who use GIS-software that doesn't support raster data or grids, as a zipped ESRI shape files. It should be noted, however, that the values in the ASCII-grids have a precision of 6 decimals while the values in the shape-file have a precision of 2 decimals. For model calculations it is therefore recommended to use the grid-version. As a service to those people who would need to know the absolute area equipped for irrigation, another ASCII-grid is available in which the area equipped for irrigation is expressed in hectares per cell. Non-GIS-users can download the map as PDF-file in two different resolutions.
Users of Google Earth can see the Global Map of Irrigation Areas V4.0.1 as an overlay by opening this file in Google Earth.
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