[OSM-dev] Layered Tiling (Mapnik)

[Frederik Ramm]

Hi,

    I am often confronted with people from the classic GIS world who 
tend to think that tiles are somehow second-class and anything "serious" 
needs to be in WMS (or, at least, OGC TMS).

Upon closer inspection, if their software supports it, most users are 
actually *better off* with a standard OSM-style tile server than with 
WMS. (If their software doesn't support it then you end up using some 
sort of tile-to-WMS rescaling which messes up the good looks.)

Until now, there were two use cases where I advised users to go for WMS 
rather than tiles: 1. if they needed lots of different projections and 
variable scaling; 2. if they needed lots of different layers (e.g. 
roads, buildings, landuse areas, waterways, POIs, ...).

I'm beginning to think that #2 need not be a reason to use WMS. Given 
the way our rendering works, it should only be minimally more expensive 
to create, say, 10 meta-tiles for an area, each with different features 
drawn on it, than just one. It would break some layering - if you paint 
roads and railways on different tiles then you can *either* display 
roads over railways or railways over roads but not - but on the whole it 
should not be too bad.

Has anyone done some experimentation in that direction? I know that 
Nop's riding+walking map uses three layers (OSM background, third-party 
hillshading, OSM foreground), and of course I've seen the grand 
ImageMagick-based TopOSM. Has anyone tried a multi-overlay tile server 
in Mapnik?

Bye
Frederik