Northing

A northing is the north–south coordinate in a projected coordinate system — the distance northward from that projection’s origin, usually expressed in metres. It is paired with an easting, the east–west coordinate, and together they locate a point on a flat grid rather than on the curved surface of the Earth.

Measured from the projection’s origin, not always the equator

Northings are measured from whatever origin the projection defines, and that origin differs between systems. In UTM’s northern hemisphere zones the origin is the equator. In the southern hemisphere a false northing of 10,000,000 m is applied so values stay positive. In the British National Grid the origin sits southwest of the Scilly Isles, again chosen so no coordinate in Great Britain is negative.

This is why a northing is meaningless without knowing its coordinate reference system. The same number refers to entirely different places under different projections.

Northing and latitude are not the same thing

Latitude is an angular measure on a sphere or ellipsoid. A northing is a linear distance on a projected plane. Converting between them requires the projection parameters; they cannot be used interchangeably.

Where you meet them

Northings appear in surveying, cadastral and engineering data, national mapping products, and any GIS working in a projected rather than geographic coordinate system.