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According to most of the answers on What is the difference between DEM, DSM and DTM?, there is a difference between a DEM and a DTM.

In particular this answer seems to offer a clear explanation of the difference between a DEM and a DTM:

A DTM is effectively a DEM that has been augmented by elements such as breaklines and observations other than the original data to correct for artifacts produced by using only the original data. This is often done by using photogrammetrically derived linework introduced into a DEM surface. An example is hydro-flattening commonly seen in elevation models done to FEMA specifications

Incidentally, a DEM is far cheaper to produce an a DTM.

So should we un-synonymize the and tags?

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Although the case for considering the terms DEM, DTM and DSM to be distinct seems reasonable to strong, for a pragmatic tagging system here, I do not think that pure distinctness of terms should be the primary reason to create new tags (or un-synonymize old ones).

To decide on a pragmatic approach for tagging questions about DEMs, DTMs and DSMs, I think we should include consideration of how commonly they are turning up in our questions:

Another consideration is whether the terms are often being applied ambiguously within those questions, and What is the difference between DEM, DSM and DTM? suggests to me that they are.

Rather than creating separate tags for the three related non-synonymous terms, I propose that we tag questions about DEMs, DTMs and DSMs using the single tag with a tag excerpt that I have just revised slightly to:

For questions about Digital Elevation Models (DEM), Digital Terrain Models (DTM) and Digital Surface Models (DSM)

The tag wiki is currently not fully aligned with this tag excerpt but if this Q&A endorses the latter then the former can then be updated.

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