Precursor - Exchange Survey

The data to be used for creating the terrain must be available. This may come either from a survey or from an existing map source. In either case, it is referred to here as a 'survey'.
The survey must provide:

	Coordinate reference system used for the survey data including the datum and vertical datum
	A set of individually identifiable points that define the terrain. Each point must have a placement that is relative to the survey datum