A new global cropland map combines multiple satellite data sources, reconciled using crowd-sourced accuracy checks, to provide an improved record of total cropland extent and field size around the world.
Knowing where agricultural land is located is crucial for regional and global food security planning, and information on field size offers valuable insight into local economic conditions, researchers said.
Two new global maps, released in the journal Global Change Biology, provide a significant step forward in global cropland information on these two topics.
The first map shows global cropland percentages at 1 kilometre resolution for the year 2005.
It was developed by the International Institute for Applied Systems Analysis (IIASA) and the International Food Policy Research Institute (IFPRI) using a hybridisation of multiple data sources contributed by many other institutes and organisations, combined with crowd-sourcing validation data where volunteers used high-resolution data to check the accuracy of larger-scale maps.
"Current sources of information on cropland extent are not accurate enough for most applications," said IIASA researcher Steffen Fritz, who led the project.
"The global cropland map is a low cost solution to fill this need," said Fritz.
"Our hybrid approach combines existing maps to produce a better integrated product than any of the individual global base maps currently available," IIASA researcher and co-author Linda See added.
The new global cropland map is more accurate, by virtue of increased agreement between different datasets on cropland cover.
The researchers used a likelihood method to quantify the level of uncertainty, using agreement between maps to assign a likelihood to each area.
"Where all maps agree there is cropland, there is a higher likelihood that cropland is present," See said.
"Getting an accurate crop map is particularly difficult in developing countries, where small-holder plots are tough to differentiate from the surrounding vegetation," said Liangzhi You, a senior research fellow at IFPRI.
The study also presents the first ever global field size map - an important proxy for mechanisation and human development.
