[Mapcss] Zoom levels: bad idea?

[Frederik Ramm]

Hi,

Chris Browet wrote:
> Yo mean the interpretation is up to the implementer? It might be 
> difficult to have consistent maps for a given style this way...

I agree to that, but...

> In this case (and in 90% of the non lat/lon-mercator projections) the 
> bbox is not orthogonal/rectangular (have a look at 
> http://en.wikipedia.org/wiki/Map_projection for some exotic ones).
> The basic assuptions of tiles is that the world representation is 
> rectangular, which is mostly not the case for projections. Which is why 
> TMS only accepts lat/lon (EPSG:4326) and mercator as projections...

... this is a non sequitur. You can use *any* projection with tiles. The 
tiling happens after the projecting; after projecting, you have the 
world on a plane and it doesn't matter the slightest bit if it looks 
like a square or like an egg - the basic ideas "zoom level 0 = world on 
one tile" and "zoom level n+1 = four times the size of zoom level n" can 
be implemented just the same. You might have large unused areas on the 
outside but that doesn't negatively affect tiling.

What you will have is, of course, that the area covered by a tile on a 
certain zoom level and at a certian lat/lon will be different between 
projections.

> The only generally "recognized" zoom levels are map scales (e.g. 1:5000) 
> which are clear and precise for everyone. 

For a raster rendering engine, they are only clear and precise if 
combined with a resolution. Whoever prepares the raster thatis 
ultimately sent to paper for the printed map, needs to know not only the 
map scale but also the resolution. If you do not know the display or 
print resolution, then there is no way you can accurately create an 
"1:5000" image.

Bye
Frederik