I’d like to get some sort of tag documented for subsea/ocean banks. These are areas of shallower ocean that don’t necessarily get close enough to the surface to count as reef or shoal in their own right. They often aren’t shallow enough to count as hazards to navigation themselves, but may be frequently avoided anyway if they are prone to shifting shoals or are home to multiple actual reefs.
17. Bassas de Pedro (2,474.33 km2, least depth 16.4 m)
Missing
Table notes:
Dogger bank (of shipping forecast fame), which currently exists in OpenStreetMap twice, once with the undocumented natural=fishing_bank and once with natural=reef (which seems like a bit of a stretch to get it rendered).
The Bahama Banks, which show up very clearly on satellite imagery due to water clarity and white sandy bottom, but are in parts deep enough for deep water harbours and cruise terminals. They contain lots of reef and shoal, but aren’t really one big reef no matter how many armchair mappers decide it would be fun to trace random chunks of them. (I’d quite like to get these mapped with something more sensible.)
In use we have:
the previously mentioned natural=fishing_bank in use 5 times and a bit too focused on a single use to me.
subsea=bankin use 8 times, usually because of an import, probably the most straightforward tag.
I’m leaning towards just documenting subsea=bank in the wiki as I don’t think there will be enough interest to go through the whole proposal process, but I wanted to see if there’s any big issues with that that I haven’t spotted.
Edit: somehow I forgot mention that the list in the table is from the linked Wikipedia article. I was hoping that one of the mapped ones would reveal a tag that I’d missed and found the results interesting enough to include.
Makes sense, and I’d be happy to support the rendering of Dogger Bank as something sensible once it is changed from being a reef, which it surely is not.
subsea seems like a good home for banks, and is due for some documentation. Looking at the common values, subsea=channel is a tag I have been longing for, with the meaning “a linear way following the deepest part of a strait”. Also used as a straight duplicate of strait it seems.
Key:subsea - OpenStreetMap Wiki is mostly redundant with natural=reef now, and it was unstructured by using different =*_reef . While it can be about ideologies and ideals, there’s no practical reason not to use natural= unless you have something as extensive as geological= etc.
I did think there would be a relevant seamark category in there somewhere, but didn’t manage to find it.
This tag seems to be used more often, but it 114/118 uses seem to be by “_import” as a way of importing LINZ data so I’m not sure it’s any more popular in practical terms.
The origin of most of the subsea=bank ones seem to be “GNS” too so there isn’t much in it in user count, but I’m still leaning towards the more straightforward tag.
The most practical reason I can see for using subsea= rather than natural=subsea_bank or natural=ocean_bank here is that if there is a bank that is particularly well known for being a good place to fish you can still use the existing natural=fishing_bank in combination with it.
It’ll also be less typing as I don’t think it will be a huge priority for preset makers.
The current wiki definition for natural=reef appears very broad (“rock, sandbar or other feature”). Before introducing other tags for “non-reefs”, the definition of a reef needs to be more specific.
The way I have generally understood it reefs are traditionally considered hard underwater features that are shallow enough to be a hazard for navigation and banks are generally notably shallower than their surrounding but not shallow enough that they are a hazard. The use of coral reef for deeper accumulations of coral has blurred this distinction a little, but I think it generally holds.
The navigation distinction is present in the documentation for the seamark:sea_area:category which appears to be lifted from modern charting practice (not that anyone should be using OSM for the kind of navigation where getting shipwrecked is a possibility). For convenience:
Category
seamark:sea_area:category
Definition
Bank
bank
An elevation over which the depth of water is relatively shallow, but normally sufficient for safe surface navigation.
Reef
reef
Rock lying at or near the sea surface that may constitute a hazard to surface navigation. See also natural=reef
Shoal
shoal
An offshore hazard to surface navigation that is composed of unconsolidated material.
I would be happy to add a note about this to the wiki page for reef as well as a bullet point under mapping caveats saying that deeper objects might be better as considered subsea=bank when I document the usage of that tag.