[OSM-talk] calculating lon/lat bounds from tilename

Matthias Julius lists at julius-net.net
Fri Jun 22 21:32:17 BST 2007


Jon Burgess <jburgess777 at googlemail.com> writes:

> On Fri, 2007-06-22 at 15:44 -0400, Matthias Julius wrote:
>> Jon Burgess <jburgess777 at googlemail.com> writes:
>> 
>> > Would the proper solution be to provide OSM tiles in a latlong
>> > projection? Mapnik is certainly capable of rendering these. 
>> 
>> What do you mean with a latlong projection?  A projection where each
>> degree has the same spacing all over the map and no matter the
>> lattitude?  That is getting more and more distorted the farther you
>> get from the equator.
>> 
>> Matthias
>> 
>
> Yes. 
>
> Whether this distortion is more or less acceptable than tiles where the
> lat/lon are non-linear across the tile depends on what you are trying to
> achieve. I think a 3D representation is the only thing that people agree
> is 'fair'. All 2D projections suffer from at least one weakness or
> another.
>
> By the sound of things people have applications which want to work in a
> nice simple square lat/lon grid. For these applications, tiles which can
> map to a lat/lon grid are probably much easier to work with than the
> current slippy mercator projected tiles. 

This is true.  You just have to be aware that it will look ugly for
higher latitudes.  At 60 deg everything will be twice as wide as it
should be (with Mercator it is twice as wide and twice as tall).

Matthias





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