Author: osm[at]petschge.de
[Added to the original trac issue at 8.55am, Friday, 23rd January 2009]

This is a very fundamental problem.

You can't (well at least you shouldn't) move the ways just to make the map look nicer. Openstreetmap is about open geo data, the maps are just one result.

Next important point is that maps have to exaggerate the width of roads (and other linear features) to make them visible on the map. This problem is more pronounced on lower zoom levels like z12, but also applies to high zoom levels like z17. Around z19 we could start to show features at their natural width.

Since we have to exaggerate the width of roads we will have roads that overlap and we will have problems at complicated intersections. If you create a map by hand, or at least fine-tune a map by hand, you can get rid of most of those problems. You can shift ways a bit, simplify intersection to show just enough details and so on. That is the look of most maps we are used to.

The big problem is: you can't really do that algorithmically. It is a really hard problem and currently I don't know any software which is able to do that for you.

So we have to resort to a simpler strategy. We draw small / unimportant ways first and draw bigger / more important ways later. This way we can be sure that important ways will always be visible. The obvious cost is that a road might obscure a walking track. For most people that is just fine.

Obviously cyclists will object to the notion that roads are more important than roads. Therefore the cyclemap rendering was "invented", which prefers cycleways over roads. As far as I know there is also a hikers / riders map planned which would probably prefer the walking track over the road. But those special renderings are not really suitable for the general map osmarender is trying to be.

Author: eliot[at]blennerhassett.gen.nz
[Added to the original trac issue at 9.13am, Friday, 23rd January 2009]

Thank you.

Replying to [comment:1 osm[at]petschge.de]:

This is a very fundamental problem.

You can't (well at least you shouldn't) move the ways just to make the map look nicer. Openstreetmap is about open geo data, the maps are just one result.

In this case the ways are estimates in any case. Perhaps moving the footway as little as 1m further from the road centre will be enough, still within margin of error.

Another possibility is that the road type should be a lesser designation. These are gravel tracks, not paved highways. E.g. change from "unclassified" to "track". A side effect is that they are rendered thinner.

I will experiment, and discuss with the original mapper.

Is there somewhere where the as-rendered width of different items is defined. E.g. unclassified road appears to be 5m wide at z17 etc?

Author: osm[at]petschge.de
[Added to the original trac issue at 12.01pm, Friday, 23rd January 2009]

Well in the case of rough estimates you might be able to change the map a little. The widths are defined in the stylesheets, but are given in terms of svg pixel which take a bit of effort to convert to sizes in meters.