[OSM-dev] How did Mapquest do the localized rendering schemes?

andrzej zaborowski balrogg at gmail.com
Wed Dec 28 08:02:37 GMT 2011


On 28 December 2011 07:48, Toby Murray <toby.murray at gmail.com> wrote:
> On Tue, Dec 27, 2011 at 12:38 PM, Stephan Knauss <osm at stephans-server.de>
>> Thanks for the pointer to the styles. Any Idea how they determine which
>> style to use for which geometry?
>> I did not see anything that looks like a way to select the one style or the
>> other based on the geographic location.
>>
>> Can you do the location check while rendering or would it be a preprocessing
>> step during import? I did not see an additional "region" column so no idea
>> how the selection was done.
>
> I thought this was the case but after a little searching, I came up
> with proof. MapQuest added this feature to Mapnik:
> http://lists.openstreetmap.org/pipermail/talk-us/2010-November/004820.html
>
> So it is apparently determined at render time. No clue how though :)

I don't know either but here is how I'd try to do this: at high zoom
levels where it's unlikely that a single tile has to use multiple
stylesheets you could run renderd with each stylesheet as a separate
layer and select the right layer at mod_tile level, I think this could
be really fast.  At low zoom levels you could preprocess stylesheets
to make a single big stylesheet with the sql queries having the
polygon checks added to them.

Cheers



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