I downloaded the urban extents grid from GRUMP (alpha). When opened in ArcGIS, there are only two values 1 and 2. What do these values mean ?
The alpha version of the urban extent mask does not include attributes. It is just a mask of urban versus rural where 1 = rural, 2 = urban. Also, -9999 values means “no data”, -9999 comes from internal “hole” polygons, typically waterbodies.