A reef is a rock, sandbar or other feature (such as coral, stromatolites...) that lies permanently beneath the surface of the water but close to the surface (permanently means at low tide for the seas).
However note that small parts of reefs may be exposed at low tide, but not the entire feature. Reefs are never exposed at high tide.
How to map
To map a reef you can just draw a line closing on itself, marking the area of the reef and tag it with natural=reef. To map larger or ring shaped reefs, use a multipolygon .
If you do not know the exact area of the reef you can map it as a node or as a not closed way .
- name=* for the name of the reef
- reef=* to specify the type of reef, for example reef=coral
This tag should not be used for:
- features that rise permanently above the water - use place=island/islet instead and add the type of soil/vegetation if you know it (sand, bare_rock, scrub...). If the area is in a sea, don't forget to add natural=coastline (not needed for a inland piece of water).
- features exposed at low tide but water covered at high tide - use the more appropriate tags between natural=shoal or natural=sand + tidal=yes (if the area is sand or gravel like for the lower part of beaches lying below the water level at high tide), natural=bare_rock/rock + tidal=yes (for rocks) and natural=wetland + wetland=tidalflat (for tidal flats, i.e. muddy areas, see mudflat on Wikipedia).
Possible tagging mistakes