Rendering natural=sand earlier on midzoom

[kocio-pl]

Related to #2654, follow up to #2722.

Another landuse type that can be rendered on midzoom on z8+ (instead of z9+), just like the forest and farmland, because there are already places where it can be quite big (=visible even on the low zoom scale) and it helps diversity.

@rrzefox: Could you add this patch too and check the performance implications?

Examples (click to see unscaled images):

Egypt, z8

Africa, z8 (converted to JPG to fit in GitHub filesize limit)
-> link to big image

[sommerluk]

Could you remove the Africa image itself from this PR description and leave only the download link to https://user-images.githubusercontent.com/5439713/29237544-a19b77fe-7f20-11e7-956c-9b9129ee4e42.jpg

It’s so big, it crash’s my browser(s) and even my image preview… 😉

Anyway an intresing image. So not much of the Sahara sand is currently mapped in OSM…

[kocio-pl]

Update - names should also render earlier, especially since these tend to be named, big areas:

Egypt, z8 (click to see unscaled images):

[rrzefox]

@rrzefox: Could you add this patch too and check the performance implications?

added and rererendered Z 8 and 9; Your example area would be roundabout here: https://osm.rrze.fau.de/map-ll-osm?zoom=8&lat=28.919&lon=27.745&layer=RRZE%20tileserver%20osm.org%20style%20tiles
Looking at rendering times of randomly selected metatiles I see no mayor performance impact (but take this with a grain of salt: This is a server rendering usually multiple tiles in parallel, sometimes live, so the fluctuation from that will be so big that a performance impact of a few percent simply isn't measurable).