[Tagging] coastline v. water

Eric H. Christensen eric at aehe.us
Wed Nov 18 20:19:51 UTC 2020

After a few days of much work, a recent collaborative project to turn the Chesapeake Bay from a nothing space outlined by natural=coastline to what we considered to be a more accurate relation of natural=water, we've received some negative feedback.

The difference of opinion seems to lie in the definition of what we're mapping.  The use of coastline is for "seas"[0] while the use of water is for "inland areas of water"[1].  Even though the Chesapeake Bay is tidal, there is no question that it is an inland waterway (it is completely surrounded by land except for the mouth at its southeast side).  The idea of using coastlines for basically creating an edge between the land and the nothingness of the ocean makes sense when, as far as the eye can see it's only water.

Now, some of the feedback that has been presented[2] is that because it is tidal it is part of the sea.  I have pointed out that many rivers and streams (and ditches!) are tidal; does that make them part of the sea?  I would not think so.  In fact, there are named seas on this planet that are not even connected to other water formations (the tiniest, according to the National Geographic, is the Sea of Marmara which has an area just less than 12,950 sq km, larger than the Chesapeake Bay).

But, tagging the Chesapeake Bay, and its tributaries, as "water" brings several benefits to the map and the users.  First, it helps identify the sections of water that exist in these areas (this can't really be done with node points as there is no way to define start and end points of an area).  There are many defined bays, rivers, and streams that make up the greater Chesapeake Bay area.  What one may see as one large mass of water is actually many smaller defined segments each with their own history.  Second, we can speed up any updates (fixes) to outlines of the polygons that happen in these water areas without having to wait for the entire Earth's coastlines to be re-rendered.  I suspect having less coastline to render would also speed up the rendering of coastlines as well?

I would like for the tagging community to clarify the different between "water" and "coastline" and when to use each.  The definition on water seems to say to use it on inland water but there seems to be, at least, and open interpretation of the word "sea" for coastline that is dragging many inland waters into that category.

Eric "Sparks" Christensen

[0] https://wiki.openstreetmap.org/wiki/Tag:natural%3Dcoastline
[1] https://wiki.openstreetmap.org/wiki/Tag:natural%3Dwater
[2] https://www.openstreetmap.org/changeset/94093155#map=10/37.1620/-76.1581

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