This study integrates global data on croplands and
urban extents using spatial overlay analysis to estimate the global area
of urban and peri-urban croplands. The global
area of urban irrigated croplands was estimated at about 24 Mha (11.0
percent of all irrigated croplands).
The global area of urban rainfed croplands found was approximately 44
Mha (4.7 percent of all rainfed croplands). This suggests urban agriculture is more important than previously estimated. Further analysis of croplands within 20 km of urban areas show that 60 and 35 percent of, respectively, all irrigated and
rainfed croplands fall within this distance range. (I have no idea why this has all appeared in capital letters, sorry!)