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

[Andy Allan]

I think you'd be better off exploring these issues on our development
list (dev at openstreetmap.org), where you're more likely to catch the
attention of the main developers. Newbies is here to help folk getting
started with mapping, and not so much for proposing new indexing
schemes for the database!

Cheers,
Andy

On Dec 25, 2007 6:31 PM, Kelly Jones <kelly.terry.jones at gmail.com> wrote:
> 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/
>
>
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