Railways should be drawn above roads (when on the same level)

[tyrasd]

Right now railways are not always drawn above streets, like here:

Here is an example where it works:

(the road and railway ways have neither the layer nor bridge/tunnel tags.)

[matthijsmelissen]

It seems related to the presence of the level_crossing tag?

[matthijsmelissen]

Also related to issue #162.

[tyrasd]

To me it looks to be induced by road classification: secondaries, primaries, etc. do overlap railways, tertiary and below don't:

[gravitystorm]

It's a feature of the z-ordering calculations in osm2pgsql.

https://github.com/openstreetmap/osm2pgsql/blob/master/tagtransform.c

I main intention of the z-ordering of the roads is to ensure that major roads are drawn after minor roads, so that the fills look OK. The bridges and tunnels aspects of the calculation are less important, since we've now ended up handling the layer tag with separate layers in the stylesheet (long after the osm2pgsql z-order code was written).

I think the value of "5" for railways is based on relative importance - at medium zooms, say, you don't want major roads obscured by railways, but railways are more important than minor roads.

Is there an inherent reason for railways to be drawn over all roads? Are they more important? Or is it just an artifact of us having thin railways and fat roads?

[tyrasd]

I see. I think you are right. Railways aren't inherently more important than roads. But on the other hand we have tramways which are always drawn above roads, so there is at least a little bit of inconsistency here…

[matkoniecz]

Rail hiding under road is causing major problem with bridges (there was an example: https://github-camo.global.ssl.fastly.net/bb7c879693194e95b9f663c07e381d800e9b6caa/687474703a2f2f632e74696c652e6f70656e7374726565746d61702e6f72672f31342f383730352f353830352e706e67 ), as on some zoom levels road is wider than bridge, what makes necessary to set layers for railway to keep it rendered above.

Also, some major roads have level crossings with railways - this design style hides it.

As major roads are wide current style may hide railway that is constructed along major road. As railways are thin drawing it on top may be better also in this situation.

[CloCkWeRX]

Previously:

• https://trac.openstreetmap.org/ticket/2863
• https://trac.openstreetmap.org/ticket/4342

[matthijsmelissen]

Resolved by #626.

[matthijsmelissen]

Confirmed as solved.