Projection metadata describe the characteristics of the spatial reference system that was used to georeference a particular dataset. If you know what spatial reference system your dataset uses, it will be much easier to register your dataset to another dataset that uses a different spatial reference system. Important components of projection metadata include:
- Map projection name
- Details of the map projection parameters (e.g., standard parallels, the central meridian, any false easting or false northing associated with the projection)
- Planar coordinate information (i.e., whether the position of a point is encoded by the distance of that point from the origin of a coordinate system or through the angle and distance from another point (a metes and bounds description))
- Horizontal datum name
- Ellipsoid name
- Vertical datum name (if applicable)
Knowing these parameters is necessary for the process of defining a projection and spatial reference system (see the Defining a Projection concept gallery item below). This link is an example of Projection Metadata (taken from the same example used in the Metadata Concept Gallery item).