Using eyes on the ground to map global cropland
How much cropland does the world have? Hard to say. Current estimates run as high as 1.7 billion hectares and as low as 1.2 billion hectares. The difference—half a billion hectares—is about five times the size of Ethiopia.
But a more precise answer may be on the way. A team of international researchers has devised a project to use the “crowd”—Internet-connected people all over the world—to develop a global map that can answer this and other important questions. According to Liangzhi You, a senior research fellow at IFPRI and part of the team behind the Geo-Wiki Project led by the International Institute for Applied Systems Analysis, this cropland map will be the most detailed and accurate ever.
Cropland information is fundamental, says You, like population information. Policymakers and donors can better target their agricultural and rural development policies and investments if they know what crops are growing where.
In recent years cartographers have developed maps by combining satellite imagery with land use data. But for many areas around the globe, these maps disagree about what type of land is there. Is that agricultural land, forest, or something else? In Europe and the United States, where large-scale commercial farms are prevalent, it’s relatively easy to identify cropland in satellite images. But this gets tricky in developing countries, where smallholder plots are tough to differentiate from the surroundings. “Grass and crops and bushes can be hard to tell apart,” says You.
Geo-Wiki incorporates current maps into the Google Earth platform. Where the maps agree, the matter is considered settled. Where they disagree, the “crowd” steps in. Volunteers select a point on the map to review. By examining satellite images or drawing on firsthand knowledge of the area, they resolve the discrepancy. In addition, a Geo-Wiki application for mobile telephones lets people on the ground take a picture that can be uploaded to Geo-Wiki along with GPS and orientation information.
Geo-Wiki is public, so anyone can access the site and contribute. To help motivate the “crowd,” Geo-Wiki used a recently concluded competition in which top contributors could win gift certificates and participate as coauthors of the scientific paper to be produced by the project. The project itself is ongoing so that it can capture changes in cropland over time.
“Our eyes are better than any satellite, but a satellite can circle the earth in a day. With Geo-Wiki our eyes can cover much more area,” says You.