[Tagging] Feature Proposal - RFC - area:highway

Tobias Knerr osm at tobias-knerr.de
Wed May 11 22:01:43 BST 2011

M∡rtin Koppenhoefer wrote:
>> If you follow the convention that each way should be drawn along the
>> center of the real-world feature, then the width of e.g. a sidewalk can
>> still be determined at any point along the road from just the single
>> outline area and the way position.
> no, if this would be possible there would be no sense at all to map
> areas. You can't see sidewalks as "just another lane", because they
> tend to be quite irregular in certain settings (unlike lanes which
> usually keep their width and have no corners and other weird points).

I don't think this contradicts my argument. Look at the cross-section of
the road at any point:

| *  .  .  .  .    *  |

The vertical lines are road area outlines, the stars are sidewalk ways
and the dots are other "lanes".

If we make the assumption that each way marks the center of that "lane",
we can easily calculate the width of the two sidewalks at this
particular cut through the road: It's 2 times the width between the
sidewalk and the area outline.

How a cross-section of a road looks will of course vary a lot along the
road - lanes, including sidewalks, might change their width, disappear
entirely etc. But that isn't a problem as long as you can determine the
road structure at each interesting point along the road.

> The point of mapping areas is to be able to map irregular street
> areas, changes in the sidewalk and similar. That's why I proposed the
> area relation: to be able to map these details, to be able to add
> topology details like kerbs and lower kerbs and similar issues.

The area relation is interesting conceptually, but it just seems so very
different from the way-based modelling we currently use for roads. I
don't believe it would work without a major redesign of our editing
tools, and I don't see OSM as a project with enough coordination to
successfully implement a major change like that if it cannot easily be
broken down into small evolutionary steps.

-- Tobias Knerr

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