[Mapcss] Zoom levels: bad idea?

[Richard Fairhurst]

Chris Browet wrote:

> Zoom levels are fine (as an alternative, IMHO) if they are very clearly
> defined in a generic/projection agnostic manner AND if scales are defined
> too.
> The only generally "recognized" zoom levels are map scales (e.g. 1:5000)
> which are clear and precise for everyone. When you buy a printed map, the
> scale is not defined by a zoom level ;-)

Yep, but most web maps are delivered in a tiled format into a  
resolution-dependent browser. In other words, the renderer has no idea  
what scale the map will be shown at. If I serve a bunch of standard  
900913 tiles at z15, I don't know whether the user will be looking at  
them on a 72dpi monitor, a 96dpi monitor, or whatever - and that  
affects the scale.

I'd suggest that we standardise on a choice of:

   |z13    - means standard 900913 zoom level
   |s2500  - means 1:2,500 scale

Renderers should support at a minimum the |s format; the |z format is  
advisable if they are likely to be used in a web mapping context.  
Renderers should make the best judgement as to scale/zoom mappings  
based on the information available to them.

cheers
Richard