Rendering surface value should reduce prevalence of using highway=track for any unpaved road. Unfortunately currently this tagging for renderer is really popular.
There are various styles typically used to depict important low quality roads:
(1) lack of fill, only casing is displayed. But it works well on maps where most roads are OK, and only some are of low quality (typical for maps of Australia with unpaved roads across the outback). In areas where all or nearly all roads are unpaved results would be weird - roads render as thin double lines. Also, there would be problems with OSM data model, as rendering of crossings and places where way is split would be poor
(2) lack of casing or dashed casing - this style is currently used for tunnels. It would make necessary to find a new style for tunnels what is not easier. Also, people would be highly confused by using of tunnel style with a new meaning.
(3) dashed fill (normal road colour & special colour) - it is style that seems the most promising and examples below show how it may work. Roads under contruction are currently using this style - it is also necessary to change it.
(4) new separate colours of fill/casing - changing only casing is not really noticeable and/or is ugly, changing colour of fill doubles number of road classes that should be distinguishable. What worse, unpaved and paved of the same class should be similar what is quite hard to achieve. This differentiation is used really rarely, with Humanitarian style as the most prominent example.
(5) display in style similar to current highway=track - this style is not working well for important roads of a low quality (there are situations where [highway=primary; surface=unpaved] is used)
(6) dashed casing & fill (normal road style & empty space) - this style works better for roads under construction. highway=construction may start using such style
Styling of unpaved roads should:
- introduce easily noticeable difference between paved and unpaved roads
- do not introduce highly busy styling
- make clear that unpaved road is worse than paved road
- do not make unpaved road more noticeable than paved one
- keep unpaved and paved road of the same class similar
on the left - current rendering, on the right possible new rendering
But situation is further complicated by fact that some roads are unpaved with set access=no/private/destination. Ideally it would be clear whatever given private road is also paved/unpaved. Unfortunately this part is not really successful.
On map above it is not immediately clear which road, if any is unpaved.
But in case of private roads it is more important that there is no access than surface value and unpaved roads with access=destination are quite rare so maybe this problem is outweighed by rendering surface value.
One thing that remains to be adjusted is how prominent dashes should be. Below are sets of images with various intensity of dashes. For each location there are four images
left: current rendering right: light dashes
left: light dashes right: moderate dashes
left: moderate dashes right: strong dashes
left: strong dashes right: really strong dashes
Unpaved primary road
City with some unpaved roads
Unpaved service roads. Such roads are very often mapped using highway=track
Paved and unpaved raceways.
City with curvy unpaved roads
Unpaved road with access=private
Unpaved road in the city
Unpaved road in suburbs
Unpaved roads in a village
Unpaved road with access=destination
Unpaved tertiary road
Currently I am planning to use moderate dashes.
Differentiating highway=trunk and highway=motorway
I am working on two version of differentiating of these road types. First keeps all road types in in white-yellow-red gradient, with an additional road class. Second is based on the German map style. Unfortunately, after days of tweaking I am still unhappy about results so I decided to avoid publishing preview.
highway=residential on z12?
flohoff proposed to keep highway=residential on z12
I love the z10 z11 residential road change. I'd like to keep them in z12 for the moment. Residentials often make one get an impression on residential areas and population density. That would get lost.
From my test (some comparison images are linked below) - rendering highway=residential on z12, less prominent than highway=unclassified improves map for locations without mapped landuse=residential. But for places where landuse=residential is mapped it is better to not render these roads.