[OSM-dev] Rendering differences between own installation of mod_tile+mapnik vs. *.tile.openstreetmap.org

[Ilkka Kaakkola]

Hi, I'm wondering what is done differently on the (a|b| 
c).tile.openstreetmap.org server compared to my own installation,  
regarding world boundaries & coastlines & especially lakes on high  
(larger scale) zoom levels.

Below is a few links to screenshots detailing what I mean, the tile on  
the left is created by my installation of OSM + Mapnik + mod_tile +  
rendered , the tile on the right is the same tile from OSM server (http://a.tile.openstreetmap.org/6/37/18.png 
)

My setup is using data downloaded recently (osm.xml , mapnik,  
world_boundaries, processed_p, Planet.osm) and osm.xml has not been  
customized for the first two example images (other than paths &  
database logins). Files have been downloaded from the places described  
at http://wiki.openstreetmap.org/index.php/Mapnik


Why is my version of the map lacking lots of detail (the big lake,  
coastline detail, scattered little bodies of water) that is visible in  
the osm generated image?

http://xe.nic.fi/~xenic/tile_problem.png

If I zoom in enough, I do eventually get the lake visible in my  
rendering (again left is my installation, right is tile.osm.org): http://xe.nic.fi/~xenic/tile_zoomed.png

Now, I tried fiddling with osm.xml to view processed_p (the more  
detailed information that does contain the lake) data on higher zoom  
levels, but I end up with a nasty grid covering the image:
<Style name="coast-poly">
<Rule>
<MaxScaleDenominator>2500000000</MaxScaleDenominator>
<PolygonSymbolizer>
<CssParameter name="fill">#f2efe9</CssParameter>
</PolygonSymbolizer>
</Rule>
</Style>

results in this:
http://xe.nic.fi/~xenic/tile_grid.png


the visible Grid seems to be made up of actual lines within the data,  
as changing the style to:

<Style name="coast-poly">
<Rule>
<MaxScaleDenominator>2500000000</MaxScaleDenominator>
<PolygonSymbolizer>
<CssParameter name="fill">#f2efe9</CssParameter>
</PolygonSymbolizer>
<LineSymbolizer>
<CssParameter name="stroke">black</CssParameter>
<CssParameter name="stroke-width">0.2</CssParameter>
</LineSymbolizer>
</Rule>
</Style>

results in this:
http://xe.nic.fi/~xenic/tile_grid_black.png


The same effect can also be seen at (for example) http://www.opencyclemap.org/ 
  , If you zoom into a global view of Finland and then change the Base  
Layer from the top-right corner to something else than OSM Cycle Map  
the various lakes disappear.

Any help / ideas to get the Mapnik rendering to match that of  
OpenStreetMap.org would be appreciated.


Cheers, Xenic