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

[Kelly Jones]

Thanks, Martijn.

Here's my thought:

 % Associate the 10,000 most important nodes w/ the QuadTile
 representing the whole world.

 % For the 10,001st most important node, associate it w/ QuadTile A,
 B, C, or D (using:
 http://wiki.openstreetmap.org/index.php/Image:Level3.jpg as my
 reference), depending on which QuadTile it's in.

 % In general: insert the nodes in importance order. Each node is
 associated with the largest QuadTile it's in that isn't already
 filled up (filled up = has 10,000 nodes).

Why this helps:

 % When mapping QuadTile ABCABCABC (for example), you first look at
 the 10K nodes in "" (the whole world QuadTile), then the nodes in
 "A", then in "AB", and so on. Of course, not all will intersect
 ABCABCABC, so you have to do some post-processing. However, you're
 only looking at 100K nodes max (at level 17, you're looking at 180K
 nodes), which isn't bad.

For ways, you'd still have to use the smallest QuadTile that serves as
a bounding box.

Any thoughts?

I thought the osm.xml imposed a partial ordering on nodes, not a
complete ordering?

-- 
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 1:36 AM, Kelly Jones <kelly.terry.jones at gmail.com> wrote:
> > This OSM map:
> >
> > http://tile.openstreetmap.org/4/2/6.png
> >
> > displays San Francisco and Los Angeles, but not the smaller city of
> > San Diego, even though San Diego is in the clip area.
> >
> > How does Mapnik know which nodes are more important than others? In
> > other words, how does Mapnik decide which nodes to render?
>
> There's an order specified in the configuration. Download the osm.xml
> file from SVN and you'll see the rules...
>
> > If OSM could impose an "importance ordering" on all nodes, we might be
> > able to generate maps very efficiently in real-time using QuadTiles.
>
> There is an importance ordering already, you just need to fix it so it
> matches what you expect.
>
> Have a nice day,
> --
> Martijn van Oosterhout <kleptog at gmail.com> http://svana.org/kleptog/