When conducting multi-factor overlay analysis or multi-index comprehensive evaluation, a common preliminary step is to standardize a collection of raster layers from various sources to a uniform 0 to 1 range. This normalization facilitates subsequent weighted overlay procedures. Theoretically, a simple linear rescaling based on the minimum and maximum values of each raster should yield results exactly between 0 and 1.
However, many users encounter a perplexing issue when using tools like QGIS's Raster Rescale tool, the Raster Calculator, or GDAL's gdal_translate command. The resulting raster's minimum and maximum values are almost, but not quite, 0 and 1. For instance, you might expect a range of 0 to 1, but the actual statistics show values like 0.006 to 0.88, or 0 to 0.99999999999999. This discrepancy can be unsettling. Drawing insights from a relevant discussion on GIS Stack Exchange, this article explores the underlying reasons for this issue and presents a more reliable workflow.