[Mapcss] MapCSS 0.2 finalization - zoom levels

Paul Hartmann phaaurlt at googlemail.com
Fri May 4 17:27:22 BST 2012

On 05/04/2012 06:13 PM, Thomas Davie wrote:
> A simple method of fixing this might be to introduce a new property
> to the canvas element – projection.
> Different projections would then pay attention to different zoom
> condition formats; e.g. if projection:merkator was specified, |z0-...
> would be expected; while if projection: OSGrid or projection:
> spherical were used, then |s25000 might be expected.

Hi Bob,

style authors should have the choice between |z... and |s..., it's too
much redundancy to specify both. In addition, I don't like the idea of
fixing the projection for a given style. There is no reason, why a style
shouldn't work for all kinds of projections.


> On 4 May 2012, at 17:03, Paul Hartmann wrote:
>> On 05/01/2012 03:59 PM, Richard Fairhurst wrote:
>>> On 01/05/2012 14:47, Paul Hartmann wrote:
>>>> In my opinion, it should be the same in MapCSS and the
>>>> definition of the zoom selector should be based on map scale
>>>> rather than on the projected coordinates in the Mercator
>>>> projection.
>>> My long-term intention for the zoom selector was that "z" would
>>> not be the only way of specifying a zoom level, but that we could
>>> also have "s" for a standard ratio scale.
>>> So:
>>> |z14-18        # "900913" zooms 14-18 |s25000-50000  # 1:25k to
>>> 1:50k
>> For a map that is displayed on screen, a scale such as 1:50k is
>> not enough, because you usually don't know the monitor resolution.
>> We could either use a scale in cm/px directly, or assume some
>> arbitrary pixel size, like 0.28 mm.
>>> I think we absolutely need to keep the z selector as it is.
>>> Otherwise, there is no way to work out what features to include
>>> in a simplified database for small-scale rendering, bearing in
>>> mind that 900913 maps represent 90% of the webmaps in use today.
>>> But offering an alternative for those who want it makes sense to
>>> me.
>> I see that this simplicity is desirable for a TMS using 900913
>> (aka EPSG:3857).
>> But it gets problematic when the map is based on a different
>> projection. Are you supposed to replicate the 900913 distortions?
>> This is hard to swallow.
>> Paul
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