On these maps, vegetation is pictured as a scale, or index, of greenness. Greenness is based on several factors: the number and type of plants, how leafy they are, and how healthy they are. In places where foliage is dense and plants are growing quickly, the index is high, represented in dark green. Regions where few plants grow have a low vegetation index, shown in tan. The index is based on measurements taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. Areas where the satellite did not collect data are gray.
The water vapor maps show the total amount of water vapor in the column of air between the surface and the top of the atmosphere on average for the month. The observations were made by the MODIS sensor on NASA's Aqua satellite. Places where the air was dry are white, while places where water vapor was abundant are blue.