[OSM-talk] Mapnik Lowzoom TIles - proof of concept

[Christoph Hormann]

On Thursday 04 July 2013, Tirkon wrote:
> [...]
> The first priority for rendering could be the admin level. Within the
> admin level at first the towns with a capital tag are rendered wirh a
> star next to the name. If this is space-kompetitiv at a given zoom
> level, the winner will be decided on the population. Then all other
> towns of the given admin level are rendered. Space-competition is
> decided first on the place tag (which could indicate independent
> cities) and then on population.

The problem about this is not how to do it in principle but that label 
placement optimization is a highly non-local problem so doing it well 
requires doing it for the whole globe at once and you would have to 
redo it every time something changes anywhere.  Even the current very 
simple approach suffers from this problem resulting in occasional cut 
off labels at tile edges.

The thing is the standard osm.org map is meant to allow near real time 
updates and compromises rendering quality for that.  But there is very 
little actual real time data in the rendering at the lowest zoom levels 
anyway - none in 0 and 1, only labels in 2 and 3.  Frederik's approach 
would bring the real time osm data to the lower zoom levels but in the 
end only few of the individual changes in the database have a visible 
effect on the map at this scale.  So it would make sense to take a 
split approach to the lower zoom levels - create a real time version 
that allows reviewing edits made to the database and a second high 
quality version that is pre-rendered periodically using techniques that 
can be more expensive.

Greetings,

-- 
Christoph Hormann
http://www.imagico.de/