Intertidal Area Import - How to tag?

Here in Norway we’re blessed with a mapping authority that provides a lot of data under licences that imply it can be imported into OSM. One such dataset describes what the mapping authority calls the intertidal zone. OSM also supports mapping of a similar concept, using the tagging tidal=yes, along with some form of landcover.

Unfortunately, there isn’t a complete match between the definitions used in OSM and the definitions used by the norwegian mapping authority. The upper limit, i.e. the coastline is identically defined, but the area considered for import into OSM reaches between 75 cm and 120 cm deeper into the sea that the normally accepted definition for the intertidal zone in OSM, hence, it is also larger than it would be expected to be in OSM. I can go into the reasons for this if anyone is interested, but it boils down to question of maritime safety.

This gives us a couple of options:

  1. We can choose not to upload such data because it isn’t a perfect fit for tag definitions in use within OSM.
  2. We can import the area tagged as tidal=yes, disregarding the fact that parts of this area dosen’t fit the definition, and will be less exposed to the air than what this tag requires. This also forgoes rendering of the areas as we don’t have an appropriate natural=* tag to combine it with.
  3. We can tag the area as natural=reef, which is also not a perfect fit. In the context of OSM we use this to describe structures strictly below the intertidal zone. Since a part of this area reaches all the way up to the coastline, this is problematic. This, however, renders nicely, without having to specify landcover in further detail.
  4. We can invent a new tag that is a generalisation (in the sense of a superset) of the two preceding options. The new tag would imply “this is at least natural=reef, but could also be tidal=yes in places”.

I’m interested in importing this data, but I need help and guidance from the community in terms of which option to go for. Of course combinations of options are also possible. If I go for option number 4, I’d still consider double-tagging with natural=reef while the new tag gains acceptance, in order to have at least something rendering in carto. Although this could be described as tagging for the renderer, I think doing so actually makes sense from a maritime safety perspective, as it effectively warns about a navigational hazard that is real.

So, for anyone who cares: What would you do in my situation?

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