Extent of available data.
The Normalized Difference Vegetation Index is an indicator of live vegetation. It was calculated at the 10m grid scale using imagery from the Landsat satellite and Google Earth Engine. The formula is: NDVI = (Near InfraRed - Red)/(Near InfraRed + Red). Because the NDVI relies on satellite imagery, it can be calculated over large extents. This makes it useful as a uniform metric of vegetation over large areas. The NDVI is also considered a useful input for some predictive landscape models.