Recommendation:

We recommend that Horizontal and Vertical (as necessary) Datum attributes be included for data in grid structures.

Recommendation Details: Locations on Earth are specified using coordinates, which are tuples of numbers that describe the horizontal and vertical distances from a fixed point, thereby pinpointing a particular place on the map at some level of precision. But knowing the coordinates is very different from being able to interpret them.

For example, the following set of coordinates marks a specific location the Earth: (36.8, -121.5, 2000.0)

When those numbers are used in conjunction with a Datum, a reference point (or set of points) against which geospatial measurements are made, the numbers can be used to identify the location by their relative position to fixed points:

Coordinate System Type: Geographic
Units: Degrees, Degrees, Meters
Horizontal datum: WGS84
Vertical datum: EGM96

In addition, having reference information also helps in converting the coordinates to other representations. Thus, the capability of accurately interpreting coordinate information relies on the presence of Datum attributes. This recommendation ensures the Datum may be found in the data product file, so that users need not search for it in external sources such as READMEs.