[OSM-talk] Sidewalk symmetry

Tobias Knerr osm at tobias-knerr.de
Mon Apr 23 17:25:12 UTC 2018

On 18.04.2018 05:03, Andrew Harvey wrote:
> highway, surface, maxspeed, maxweight, maxheight, width, oneway, access,
> lanes, turn:lanes, lit, parking:lane:left, parking:lane:right,
> parking:condition:left, parking:condition:right,parking:lane:left:type,
> parking:lane:right:type, etc.

The percentage of roads tagged with all these details is vanishingly
small, and will likely remain so for at least another decade.

At the level of detail that's realistically achievable in the medium
term, sidewalk tags make a lot of sense: They're easy to use for the
common case (where sometimes not even the existence of sidewalks is
mapped yet), and still allow for micromapping in pockets of unusually
high data quality.

> I realise editors can and do abstract some of this, but if we can put
> all those sidewalk attributes on their own ways it makes it much easier
> to map by reducing the complexity of the highway centerline.

Comparing the mapping styles solely based on ease of mapping would only
make sense if separate ways were able to express the same information
contained in sidewalk tags.

That's not the case, though: With separate sidewalk ways, it's
impossible (in the general case) to figure out which road section that
sidewalk way belongs to.

Not having this basic information available makes separately mapped
sidewalks unusable for entire categories of applications – sometimes
leading to worse outcomes than not having the sidewalk mapped at all.
And while you could fix that issue with relations, this would clearly
not be easier for mappers than using sidewalk tags is.

As for the original question: sidewalk=separate seems like an attempt to
solve the aforementioned issue, but it does not actually achieve this
goal – it only tells you that *some* sidewalk way belongs to this
section of road, but does not help you to find out *which* sidewalk way
that is. As such, it's not a very useful tag, and not a compelling
reason to map asymmetric real-world situations in a symmetric way.

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