[OSM-dev] JSON/GeoJSON output format for 0.6 api

[Tels]

On Thursday 04 June 2009 19:48:30 you wrote:
> 2009/5/31 Frederik Ramm <frederik at remote.org>:
> > Hi,
> >
> > Tels wrote:
> >> Well, one could fetch the data at z17, see it is below some
> >> $ARBITRARY_THRESHOLD, zoom out to z16m, fetch again, and if still
> >> below $THRESHOLD, repeat it until either there is too much data
> >> (display message) or the user-requested zoomlevel was reached.
> >
> > I think the tiles at home folks already keep a database that says how
> > complex each level-12 tile is. So if we were not so busy telling
> > them how they're technologically backwards and how their whole
> > project is rubbish, they might just give us that.
>
> Each t at h user uploads a tileset at z12, which is indeed a pretty good
> indicator of the complexity of the area, see this heatmap rendering
> of the world at z12 from the t at h data:
>
> http://u.nix.is/~avar/osm-heatmap-black.png
>
> I made if after requesting the z12 tileset sizes on the t at h list:
>
> http://lists.openstreetmap.org/pipermail/tilesathome/2009-May/005859.
>html
>
> The code to generate it is under applications/rendering/tah-heatmap
> in SVN:
>
> http://trac.openstreetmap.org/browser/applications/rendering/tah-heat
>map/README
>
> In particular the parse-filesize.pl script in that directory converts
> ls -R format provided by spaetz to an easy-to-use CSV format, e.g.:
>
>   0000,1042       158211
>   0000,1043       203915
>   0000,1055       172469
>   0000,1056       80728
>
> t at h currently has around a million z12 tiles, or ~5.6% of potential
> z12 tiles:
>
>   $ wc -l tile-sizes.dat
>   937254 tile-sizes.dat
>
> It would be easy to make a web service which kept these tile sizes in
> a hash table and told e.g. Potlatch whether or not the z13 tile it's
> requesting is part of a z12 area that's say 10 times bigger than the
> median z12 tile. Which should cover the yellow/read areas on the
> above heatmap.

If such a webservice is made public, I could use it to determine wether 
an area of 0.1° or 1° should be requested.

However, getting a server that can respond to API requests in real-time 
(e.g. saturate the download link) would be the preferable situation - 
after all, all the data needs to be downloaded for rendering, anyway. 
(Rendering only half the area the user wants to see is useless :)

All the best,

Tels

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