Since the long thread I started about multipolygons [1 <https://lists.openstreetmap.org/pipermail/tagging/2018-October/040062.html>] is sort of winding down, I thought it best to start a new one to discuss something I've been doing since learning from that thread of the amazing power of the multipolygon data structure. Alaska has hundreds of bays and straits that have been added to OSM as nodes many years ago via an import (Tiger?). The nodes contain useful information but because they're only nodes cannot provide any visual representation of the size or extent of bigger bays and straits. I've begun to use multipolygon relations to show them more prominently using sections of coastline as the ways and then drawing a connecting way across the mouth of the bay or strait to complete the outer ring. This structure then defines the bay and when rendered it shows up nicely on the OSM slippy map.
However, this method means that under certain circumstances some of those ways end up as members of several multipolygons. For example, the coastline might be part of a boundary, and in addition define a wooded or wetland area so it might be confusing to new mappers who might be put off by the complexities, as I was for a long time. That's one consideration. The other is the question about using this technique to map truly large bays like Cook Inlet. This is the reason I'm posting this question. Here is the first paragraph of the Wikipedia entry for the Inlet: Cook Inlet (Dena'ina: Tikahtnu) stretches 180 miles (290 km) from the Gulf of Alaska to Anchorage in south-central Alaska. Cook Inlet branches into the Knik Arm and Turnagain Arm at its northern end, almost surrounding Anchorage. On its south end merges with Shelikof Strait, Stevenson Entrance, Kennedy Entrance and Chugach Passage. So, I could mouse along the coastline adding pieces of it to a new relation until I have the entire Inlet surrounded, then draw a way from Elizabeth Island on the east side to the other side to define its mouth. I copy the tags from the existing node to the multipolygon and delete the node. But with a water body the size of Cook Inlet, that's a lot of work. I mapped Cook Inlet's Turnagain Arm [2 <https://www.openstreetmap.org/relation/8921978#map=9/61.1074/-149.5541>] the other day and it involved adding 14 ways as outers. How many will a multipolygon covering the entire Cok Inlet require? I was thinking it would be much easier and perhaps even better to just draw an approximate shape consisting of maybe 20 or 30 nodes, big enough to define the area and cause it to render, but easy to draw and without involving any multipolygons. The issue here is admittedly one I am pursuing to get these water bodies to render in a manner proportional to their size and I suspect that many will be against it on that basis alone. Still, I thought it worthwhile to mention my idea here and see what you think about it as a "shorthand" solution. Besides, I'm betting some other useful information will issue from the discussion. Dave [1] https://lists.openstreetmap.org/pipermail/tagging/2018-October/040062.html [2] https://www.openstreetmap.org/relation/8921978#map=9/61.1074/-149.5541 -- Dave Swarthout Homer, Alaska Chiang Mai, Thailand Travel Blog at http://dswarthout.blogspot.com
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