render tracks as solid line on z13, z14 - fixes #1591

[matkoniecz]

idea by @imagico
start using @track-grade[12]-width-z15

Makes map less busy and crowded, makes tracks visible more than footways, geometry of tracks is more readable, removed dead code. No longer fully displaying tracktype at z13 z14 (what anyway was hard to read except in places with long, straight tracks) is a bad side of this change.

https://cloud.githubusercontent.com/assets/899988/9870378/ad86a6f2-5b8b-11e5-8ea7-41c4dfbc2c79.png (waterway=dam glitch is a data error that I already fixed)

https://cloud.githubusercontent.com/assets/899988/9870380/ad885650-5b8b-11e5-8d52-5e881a836d10.png

https://cloud.githubusercontent.com/assets/899988/9870379/ad8814ce-5b8b-11e5-8721-cfe37aab5112.png

https://cloud.githubusercontent.com/assets/899988/9870381/ad895a78-5b8b-11e5-94d9-acec5c760f72.png

https://cloud.githubusercontent.com/assets/899988/9870382/ad8d548e-5b8b-11e5-9dd9-ad0c077851f9.png

https://cloud.githubusercontent.com/assets/899988/9870383/ad8e6400-5b8b-11e5-9736-75ffdd776fd8.png

[imagico]

That is slightly thicker than in my example (which used line-width 0.25) which probably means it will appear stronger than highway=service on dark backgrounds at z13 - see example on #1591 (comment) at the bottom right. Maybe using a smaller width at z13 than at z14 would be a good idea - this would also weaken the abrupt change in appearance between z12 and z13.

In principle the same idea could also work on footway/cycleways - see #1748, but this will not really be feasible without solving the color issues first - see also #1765 (comment)

[matthijsmelissen]

I like the way the new z13/z14 look, but I don't like the user experience when zooming from z14 to z15. What used to be a solid line (which gives a relatively important impression) suddenly becomes a dashed, much less important line. It gives the feeling that what looks to be a nice paved road from far away suddenly becomes a muddy track when having a closer look. I'd be inclined to reject this PR.

[imagico]

I think this is an inevitable consequence of less differentiated rendering at lower zooms. We are very used to the primary measure of data reduction at low zooms being the omission of features but in principle unifying different renderings is a proven technique as well and this always leads to emphasizing some things and weakening others. IMO there is nothing wrong with that.

Two things could be considered though:

• generally making the lines weaker/thinner (i already suggested that)
• using slightly different colors depending on track grade. The idea is creating a kind of color mixture between the track line color and the casing color (which dominates the higher track grades at the higher zooms). Keeping the tracks well visible at z14 and avoiding a reduction in visual strength from z14 to z15 at the same time will hardly be possible though.

[matkoniecz]

Also, not rendering grade5, grade4 tracktypes at z13, z14 would be weird with rendering footways at the same time.

[kocio-pl]

I think @imagico has a point: it's nice to be consistent, but not at all cost. Look at the airport: it's a plane icon on lower zoom, which disappears on higher zoom levels and instead there are some violet areas. Or the trees which are just a green points which become brown dots with green circle around. So we have examples of different rendering on different zoom levels and I think this is a valid solution.

[imagico]

Does this mean the general idea of rendering tracks without dashing at the lower zooms is rejected?

[matkoniecz]

No, though it would be necessary to address problems mentioned here (track vs service, probably less wide track for grade5, grade4).

I am not entirely sure whatever it will work.