[Tagging] Way inside riverbank

Torstein Ingebrigtsen Bø torsteinibo at gmail.com
Mon Apr 13 13:06:03 UTC 2015


I'm currently importing topological data of Norway to OSM. From the data
set we have riverbanks; however, we do not have the deepest middle way as
required by the wiki [1]. This middle line is therefore drawn manually.
This is a time consuming (and dull) job. For one municipal it takes around
5-10 hours to draw all these lines, in Norway we have 428 municipals.
Drawing all these middle lines will slow down the time to import everything
dramatical. I am therefore curious of what is the benefits of this line. Is
it really necessary or is it a "nice to have"?

Some disadvantages with this middle way are:
- The line add redundancy. I guess that many add this line such that it is
inside the multipolygon of the riverbank. Doing so the added data is only
the direction of the river. (Other tags may be added to the multipolygon.)
- Sometimes people draw the line wrong or forget to update it when updating
the multipolygon. I have seen "middle" lines outside of the multipolygon
(either inside islands or outside of the multipolygon). This gives false
islands and splitting of islands when rendered.
- A similar way can be generated, if direction and deepest point is not
required. This comes as a fact of the first point and removes the
previously mentioned problem.
- For routing purposes this is not needed. (I have not seen any practical
marine navigation/routing implementations yet, either.) Routing algorithms
may also represent a riverbank as a node (or multiple nodes). The same
problem occurs for lakes where it is not required to have a middle way for
- The direction of the river is seldom used. The direction of a river is
seldom (or never?) rendered in any map. It is implicitly shown (e.g., by
contour lines).
- Specifically for the import of Kartverket N50 [2], this requirement is
slowing down the import process dramatical and import of other data of more
current value are delayed. This is therefore also a question of
prioritizing data to be imported.

I therefore propose to make this middle way in riverbanks recommended (when
the deepest way is known), not required.

[1] http://wiki.openstreetmap.org/wiki/Tag:waterway%3Driverbank
[2] https://wiki.openstreetmap.org/wiki/Import/Catalogue/N50_import_(Norway)

Best regards,
Torstein I. Bø
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