NODATAvalue

NODATAvalue refers to a designated data value used in raster datasets to represent missing or undefined data within a grid. It serves as a sentinel that is not a real measurement, enabling GIS and remote sensing software to distinguish valid grid cells from gaps, masked areas, or areas outside the sensing extent. The term appears in variations such as NoData and missing_value, and is used across multiple formats and tools.

Implementation and formats vary, but the core idea is consistent. In GeoTIFF and other raster formats, a specific NoData value is stored in metadata or headers (for example, the GTiffNoData tag in GeoTIFF). ENVI and Arc/Info ASCII grids use their own headers to designate a NoData value. NetCDF uses the _FillValue attribute to indicate missing data, while HDF formats use a fill value. Some floating-point datasets can use NaN to indicate missing data, but many formats and processing tools rely on an explicit NODATA value defined in metadata. When a NODATA value is present, most calculations, statistics, and display operations ignore those cells or treat them as masked, and results may be undefined or designated as NODATA when all inputs are missing.

Practical considerations include choosing a sentinel that does not occur in valid data, ensuring consistent usage across files, and maintaining the NODATA setting through processing and reprojection. Users should verify that software correctly interprets NoData during analysis, masking, and visualization, and be aware that some operations may propagate or alter NoData depending on the workflow and data format.