Coordinate reference system

A coordinate reference system defines how coordinates identify locations on Earth by combining a coordinate system with a datum. It may also specify a map projection and units.

Geodetic datum: A model of Earth's size, shape, and position that provides a reference for geographic coordinates. A datum anchors the CRS coordinates to a model of the Earth.
Coordinate transformation: A mathematical operation that converts coordinates between reference systems. It converts positions between CRSs while accounting for their differing definitions.
EPSG Geodetic Parameter Dataset: A registry of coordinate reference systems, datums, transformations, and related geodetic parameters. Its identifiers provide widely used labels for specific CRSs.
WGS 84: A global geodetic reference system used by GPS and many geographic datasets. It is a widely used global CRS, unlike regional systems tailored to local accuracy.
Coordinate system: A rule-based system that represents positions using ordered values such as latitude and longitude. The CRS uses a coordinate system to express positions numerically.
Datum transformation: A conversion between coordinate datums, often using parameters or grid-based corrections. It handles the datum differences that can shift coordinates between CRSs.
Universal Transverse Mercator: A global mapping system that divides Earth into sixty six-degree longitude zones using Transverse Mercator projections. Its zone-based projected CRSs support mapping and measurement across much of the world.
NAD83: A geodetic reference system used primarily for mapping and positioning in North America. Its regional reference frame differs from global systems such as WGS 84.
Map projection: A mathematical transformation that represents locations on a curved surface on a flat map. Projected CRSs use this transformation to express locations in planar coordinates.
Helmert transformation: A coordinate transformation using translations, rotations, and scale changes between reference frames. It is one method for transforming coordinates between compatible geodetic datums.

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