[OSM-dev] [Mapnik-users] How does Mapnik know which nodes are "important"?

[Kelly Jones]

Martijn,

That's great for "zoom level 17" tiles where you always want to
display everything in the bounding box.

For "zoom level 11" (for example), there are probably millions of
nodes in the tile, and you can't map them all (most are too
unimportant to be mapped).

By using QuadTiles, you only have to look at 120,000 nodes (10,000
nodes each for the QuadTile and all of its parents) to determine what to
map. Of course, you could use this in conjunction with spatial
indexing to make things even faster.

This scales well: the number of nodes you look at to render a "zoom
level 11" tile remains constant at 120,000 (or less if the tile and
its parents are fairly blank).

Note: at Andy Allan's suggestion, I've moving this thread from
'newbies' to 'dev' (dev folks, please see the newbies archive for the
first part of this thread). This message is cc'd to both lists, but
future messages will go just to the 'dev' list. Sorry about the
confusion.

-- 
We're just a Bunch Of Regular Guys, a collective group that's trying
to understand and assimilate technology. We feel that resistance to
new ideas and technology is unwise and ultimately futile.

On 12/25/07, Martijn van Oosterhout <kleptog at gmail.com> wrote:
> On Dec 25, 2007 7:31 PM, Kelly Jones <kelly.terry.jones at gmail.com> wrote:
> > I thought the osm.xml imposed a partial ordering on nodes, not a
> > complete ordering?
>
> I'm not sure why we need anything with quadtiles. Mapnik uses spatial
> indexes so it has a complete list of every node in the given area very
> cheaply. The osm.xml imposes a total order, so it renders them in the
> order specified...
>
> Have a nice day,
> --
> Martijn van Oosterhout <kleptog at gmail.com> http://svana.org/kleptog/