[Openstreetmap-dev] Cache the whole world.

[Mikel Maron]

> This computation surely is part of both the viewer and the edit 
> applet.  But with tile URLs ending in e.g. 
> BBOX=14.23818,57.84534447446815,14.282125,57.857036747911096
> one might raise questions about rounding errors.  There is no 
> point in invalidating the cache for a URL where the last decimal 
> differs, because that is a different URL.  Perhaps a %.5f format 
> should be used for the URLs?  Or something even smarter?

Rounding is sensible, though %.5f might be a bit too rough. 
And also insuring that the editor and the slippy map request the same tiling (they don't currently).

Aside, this is why tiles are commonly referenced by index, rather than extent, on many mapping providers. It might be a good idea for OSM at some point, but just doing the rounding with a consistent tiling is easy for now.

> There are cases where zoom=16 is more useful than zoom=15 in the 
> edit applet, e.g. where a bike path runs close to a road.  But I 
> have never found any use for zoom=17 or 18.

The slippy map is currently limited to zoom 20! 
What is the maximum zoom necessary to clearly view a dense network of streets, such as Soho in central London?

> Editing is only allowed from zoom=14 and up, and we currently draw 
> roads only from zoom=11 and up, so there aren't so many levels. 
> But one would have to consider that some map updates will touch 
> more than one tile at each zoom level.  I have no idea if the 
> Squid API allows more than one URL to be invalidated in each call. 
> Perhaps one can invalidate the cache for entire areas at once, 
> e.g. by specifying wildcard patterns for the tile URLs:  
> BBOX=14.3*,57.4*,14.3*,57.5* ?  That would take care of all zoom 
> levels too.  Does anybody know?  Google hits indicate that "Squid 
> wildcard purge"  is a much desired functionality.

purge is a command line tool for, yup, purging squid. It can take regular expressions for file names.
http://www.wa.apana.org.au/~dean/squidpurge/

-Mikel