[Tagging] More large feature problems: Seas, Bays and Straits

Joseph Eisenberg joseph.eisenberg at gmail.com
Thu Apr 18 13:42:32 UTC 2019

Either seas should be mapped as areas, or should bays and straits
should not be mapped as areas. Which is the best option?

Right now, mappers are changing seas to bays and mapping as large
multipolygons to get them to render. In the past year the number of
natural=bay relations has increased from 2,000 to almost 5,000, while
the number of nodes only increased from 45k to 46k. Relations tagged
natural=strait increased from 290 in March 2018 to 945 today.

This happened after bays and straits mapped as polygons were rendered
at low zoom levels in the Openstreetmap-Carto style. The rendering
change also encouraged mappers to use natural=bay for very large
features that are called a "gulf" or "bay" even though they are larger
than the average "sea".

The wiki page for place=sea has said this since 2011: "A large body of
marine water and part of an ocean: seas, gulfs, bights and very large
bays such as the Bay of Biscay."

Yet the Bay of Biscay is now mapped as a multipolygon tagged
natural=bay (likely so that it will be rendered at low zoom levels).

The original wiki page for place=sea only recommended using a node.
Another users added a suggestion to map with a multipolygon, but the
list of acceptable objects was not changed to include "area" until
January 2018. At that time, there were over 120 place=sea mapped as
nodes and less than 20 mapped as relations (see
https://taghistory.raifer.tech). Now there are 68 place=sea nodes and
63 place=sea relations.

Clearly, a few mappers have spent a good deal of time changing bay,
strait and sea nodes to multipolygons in the past several months.

I am thinking of changing the place=sea wiki page back to the earlier
version that only recommended mapping as nodes, because I cannot
download and manage these new huge relations.

Also see: https://github.com/gravitystorm/openstreetmap-carto/pull/3750

However, perhaps others disagree?

I also think that if seas should be mapped, large bays should also be
mapped as nodes rather than large multipolygons.

(Straits and narrow bays like fjords can also be mapped as linear ways)

More information about the Tagging mailing list