[Tagging] How to tag named group of named water areas?

Dave Swarthout daveswarthout at gmail.com
Fri Nov 2 00:04:47 UTC 2018

Putting aside the discussion about type for a moment, this topic relates to
a discussion I'm having with a user about tags and multipolygons,
specifically where the tags go, so I believe it fits into this discussion.
I removed the tags from the ways for a section of the Trans Alaska Pipeline
(TAP) because those same tags were on the relation itself. The user asked
in a changeset comment why I had done that. I replied that IMO, any tags
that applied to the pipeline as a whole belong on the relation and need
not, indeed should not, be repeated on each way. The TAP is 1300 km long,
has countless bridges and sections where it is underground and then
overground. The only tags that should appear on the ways themselves are
attributes of those ways, for example, location=overground or
location=underground, and tags for bridge and layer. Everything else,
Wikidata, substance=oil, man_made=pipeline, etc, should appear only on the
relation. The folks who added the pipeline mostly via Tiger imports many
years ago tagged both. When I would occasionally add or replace a section,
I was always careful to copy all the tags from a neighboring section to the
new section. Now, I think that is incorrect.

If those tags appear on each way in addition to the relation, maintaining
any consistency in the tagging on this beast would be almost impossible. I
have done quite a bit of re-aligning of the TAP over the years as our
available imagery improves but have always been tentative about removing
those redundant tags thinking I would get around to it someday. In fact, it
seems apparent that this is one major reason relations were invented,
especially for objects like routes — to ensure tagging consistency and
connectedness between the many individual member ways that comprise the

So, what is the correct and accepted way to tag something like the TAP?


On Sat, Oct 13, 2018 at 7:17 AM Kevin Kenny <kevin.b.kenny at gmail.com> wrote:

> why not a multipolygon? I agree that you don’t need additional tags for a
>> group relation, just type=group, a name and the members, but for a site you
>> would need something that describes the site, a tag for a group of water
>> areas, so as long as all the members are areas (or parts), a multipolygon
>> would be better.
> When the lakes themselves are complex multipolygons with many islands,
> repeating that data for the group is likely to be a maintenance nightmare.
> (I know this from curating boundary=protected_area relations that include
> partial shorelines on such lakes. It's especially fun when the boundary
> splits islands.)
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Dave Swarthout
Homer, Alaska
Chiang Mai, Thailand
Travel Blog at http://dswarthout.blogspot.com
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