Mapnik bug tracking has moved to GitHub, the new upstream bug URL is

https://github.com/mapnik/mapnik/issues/13

I tested with Mapnik 2.0.0: the bug is still there! (i.e. street name does not appear in short streets)

Keep in mind that 25000x25000 pixels is roughly 2.5Gb (as ABGR) of raw image data, giving a clue as to why cairo refused to save Rennes at z=18 to PNG.

Doesn't crash: ./ocitysmap-render -z 18 -c Rennes -f pdf
Crashes: ./ocitysmap-render -z 18 -c Rennes -f png

Backtrace gives the impression that either Cairo itself, or libpng as used by it can't handle 22750x24780 pixels. Which isn't surprising, entirely. I'll copy/paste the PDF rendition into the gimp and save as PNG, see what it does.

I'll also investigate backends for Cairo other raster formats than png. Perhaps it can be made to render to bmp or tiff, have ocitysmap not crash on zoom level 18, then run: optipng -o7 /tmp/result.bmp ?

I'll see if I can find some time later this month to do one of the following, or both:

- Implement ./ocitysmap-render -z auto
(auto mode would bump the zoom level to 17 or 18 if the area covered by the map is below certain thresholds, e.g. <25km2, zoom 17)

- Investigate Mapnik stylesheets, as per Dmentré's suggestion on #maposmatic.

dmentre: I see the bug has a milestone of 0.80 on mapnik's trac, did the 0.70-rc do anything at all in regards to labels being dropped?

Here is the part of osm.xml that handles the residential and unclassified streets at zoom level 16 :
<Style name="roads-text">
[...]
    <Rule>
      <!-- ici -->
      <Filter>[highway] = 'unclassified' or [highway] = 'residential'</Filter>
      &maxscale_zoom15;
      &minscale_zoom16;
      <TextSymbolizer name="name" fontset_name="book-fonts" size="9"
      fill="#f00" halo_radius="1" spacing="300" placement="line"
      avoid_edges="false" allow_overlap="true"/>
    </Rule>

But we are in the case where the street name is longer that the line that supports it.

Unfortunately, this is a known issue in current Mapnik: Mapnik cannot render street name longer than the corresponding line. See this a recent thread:
  https://lists.berlios.de/pipermail/mapnik-users/2009-December/thread.html#2584

The bug is known in Mapnik: http://trac.mapnik.org/ticket/13

It's the street from the "Quai de la Prevalaye" to the recycling POI. Definitely a zoom issue. There's a dilemma here: what do we do with streets whose names aren't displayed on the map? I don't think we should remove them from the index, since the square indication can still help locate the street. But we also can't put the names of all the streets in the city as they sometimes don't fit.

I think this is a low-priority problem since the map and index, as-is, can still provide helpful information to locate the street and direct the user into the right 500x500m square. Finding the street then is not as hard.

Also, this specific problem can be solved by the "downtown" zoom box, which is a feature we haven't yet implemented.