What is a "Nodata value"
From AWF-Wiki
A nodata value simply is a pixel value in a raster map representing no information. It is not to be confused with a pixel value of 0 (zero).
E.g. in a map with temperatures of a surface in °C, a pixel value of 0 represents a temperature of 0 °C, while a nodata-pixel simply represents a part of the surface where no information on the temperature is available.
