Now, the Latest Global Map of Irrigation Areas (Ver. 4.0.1) is available as a free download. The map shows the amount of area equipped for irrigation around the turn of the 20th century in percentage of the total area on a raster with a resolution of 5 minutes. The area actually irrigated was smaller, but is unknown for most countries. 
A special note has to be made for Australia and India where the map shows the total area actually irrigated. This is due to the fact that statistics collected in Australia and India refers to actually irrigated area as opposed to statistics with area equipped for irrigation which is collected in most other countries.
An explanation of the different terminology to indicate areas under irrigation is given in the glossary. Visit here for more details.
Source: SDI-LAC
