[Tagging] Sorting waterway relations?

Colin Smale colin.smale at xs4all.nl
Thu Feb 27 08:55:39 UTC 2020


On 2020-02-27 01:47, Joseph Eisenberg wrote:

> When you make or sort a relation of type=waterway, do you check if the
> source or mouth of the river is first on the list of ways?
> 
> Another user just suggested that the spring/source of the waterway
> should start the list, then the mouth of the river at the ocean (or
> where it empties into a larger waterway) should be last. This practice
> has not been followed in the areas where I have mapped.
> 
> https://wiki.openstreetmap.org/wiki/Talk:Relation:waterway#Sort_order.3F
> 
> Is this done in your area?

In general there is no real need to sort the members as the geometry can
be reconstructed by chaining the end nodes. If it was semantically
important, we should be scanning for and flagging up waterways with
out-of-order ways. The fact that we are not, shows that the ordering of
the ways is not essential for a correct geometrical
interpretation....QED 

As a consequence of some mappers desire to share ways between relations
of unrelated types (e.g. waterway and admin boundary) it is possible
that re-ordering the members of one relation, causes the members of
another relation to become out-of-order. If we all use separate ways
with shared nodes, the relations can be re-ordered without causing
collateral damage. 

It is accepted that a way has a direction, which is sometimes
semantically significant (water flow direction, one-way streets etc) and
sometimes not. Getting the ways into a particular order is of course a
different subject to pointing the way in the right direction. Once again
I appeal to mappers to use separate ways (with shared nodes) for
different concepts, even if they are co-linear, to allow for the
direction of the ways to mean different things in different contexts.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/tagging/attachments/20200227/b8e917be/attachment.htm>


More information about the Tagging mailing list