Conversation so far:
where might a real estate legal description most likely include a datum
In today’s real estate world, the most common use of a datum is found in a metes and bounds legal description of a property.
where else could the datum information be used
Condominiums located on upper floors or lower floors may be described in reference to a datum, which is a point, line, or surface from which elevations are measured.
why is datum necessary
Housing contracts and documents require a legal description of property that is legally sufficient, meaning that the description would allow a competent surveyor to delineate the exact boundaries.

Question: who prepares the descriptions
Self-contained rewrite: who prepares the legal descriptions of property