qgis-core-coordinate-systems
Use when handling coordinate reference systems, transforming coordinates, or measuring distances/areas. Prevents silent data corruption from wrong CRS assignment and lat/lon coordinate order confusion. Covers CRS creation, coordinate transforms, datum transformations, distance measurement, and EPSG database. Keywords: CRS, EPSG, coordinate transform, projection, QgsCoordinateReferenceSystem, datum, QgsDistanceArea, reprojection, wrong location, map shifted, coordinates don't match, set projection.