[Talk-GB] Underground Pipelines
eda at waniasset.com
Mon Nov 9 18:07:39 GMT 2009
Isn't this analogous to the flow in rivers? In some cases the mapper will know
which way the water flows and can make the way point downstream and tag it
somehow. In other cases the river may have been drawn by tracing a satellite
photo or old map over a small area, and the person doing the tracing doesn't
know which way is downstream.
(With pipelines there is a third case: known to be used in both directions.)
I agree that it might be best to keep the tag 'oneway' for legal
restrictions, and use a different one for the direction of flow. After all
it is usually legal, if more difficult, to row a boat upstream.
In rivers, we know that there must be some fixed direction of flow, the only
question is whether the direction of the way can be trusted to give it.
This argues for having a tag whose presence (as 'yes') would confirm that
this river's direction has been surveyed and matched with OSM. If the tag
is not there, then you don't know one way or the other whether the direction
of the way matches the flow of the river.
For pipelines, the possibilities are one-way, two-way, and don't know. Again
it is cleanest to represent don't know as the absence of a tag.
There are also canals and other long stretches of water which do not have
a current at all (or only a negligible one).
Perhaps 'flow' could be used, with the following convention
(missing) direction of flow, if any, not known
flow=yes direction of flow follows the direction of the way
flow=two_way can flow in either direction (pipelines only)
flow=no there is no significant flow or current in this body of water
(I'm not sure if flow=no would ever get used, it's already implied by
waterway=canal, but perhaps there are waterways which are not canals
but aren't flowing streams either.)
Ed Avis <eda at waniasset.com>
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