UN - Geographic Information Systems
The conversion of digital spatial data from one coordinate system to another through translation, rotation and scaling. Transformation is used to convert digitized digital map data from digitizer units (e.g., centimetres or inches) into the real-world units corresponding to the source map’s map projection and coordinate system (e.g., metres or feet). See also "Georeferencing".
United Nations, "Handbook on Geospatial Infrastructure in Support of Census Activities", Department of Economic and Social Affairs, Statistics Division, Studies in Methods, Series F No. 103, New York, 2009