[OSM-talk] How do I tag this road in OSM

[Wollschaf]

On Tue, 01 Aug 2006 11:28:06 +0200, Thomas Walraet wrote:

> Other possibility :
> - Ways become the physical representation of the word. multi line
> (collection of points).
> - We can still group them for tagging.

We would have to split the way every time a bridge, tunnel, paving change
or lane number change comes around. This system is good for areas where
several ways share the same nodes (segments at the moment), but have
different properties. It's bad for ways which change properties frequently.

A collection of points has to be sorted (which node at which point) to get
a sense of direction. The complete way would have to be reversed if a
oneway property changes. New nodes have to be inserted at the right point.
Things get complicated.

Segments do not have the same problems, as they already define a
direction, and may be not in order at all.

Grouping of way segments ( there the segments are again) would be a
necessity to work with that kind of ways. I dont't see that as a problem,
as (very) long ways are not so good to work with at the moment, either.
We need that feature, whatever possibilty we choose.

In my opinion we should keep segments, and add a possibility to group ways
for longer roads. Segmens can still contain physical properties (those
belong to segments), while ways define logical properties. I believe it
would be best to strictly divide this kind of information.

A segment could contain the properties Road Type/Class (A-F),
road surface, road direction, lanes. If theres a cycleway sharing the
segment, the physical properties of it should be tagged on the segment,
too. If there's a footway with stairs on the same segment as the road,
this is also a property of the segment (which can be made shorter to
acommodate the length of the stairs).

Naming of Road, ref, speed limit, usage permissions etc. belong to the
way. Ways are split when administrative categories change.

For a motorway, this would mean a way would have to be split every time a
speed limit changes, or an exit comes around. Those are usually numbered
and could be used to define a name for the way segment. You wouldn't have
to split a way for a tunnel, lane change or bridge, as this changes
nothing of the logical / administrative properties.

Ways can automatically be grouped by their ref (which in this case had to
be localized, i.e. ref=de:A5) as different countries might use the same
reference scheme. If no ref exists (local roads), ways have to be grouped
manually which is not a big deal.

Using this scheme, it is possible to render administrative maps (using way
information) or topographical (physically more accurate) maps using just
segment information. Or best, a combination of both.

Wollschaf