Scale factor at equator (a multiplier for reducing a distance obtained from a map to the actual distance along the equator), when subfield $a contains the text Mercator. Scale factor at center line (a multiplier for reducing a distance obtained from a map to the actual distance along the center line), when subfield $a contains Oblique Mercator.Scale factor at central meridian (a multiplier for reducing a distance obtained from a map to the actual distance along the central meridian), when subfield $a contains Transverse Mercator. Scale factor at the projection origin (a multiplier for reducing a distance obtained from a map to the actual distance at the projection origin), when subfield $a contains Polar stereographic. Horizontal coordinate system. Map projection.