Mapnik errors around zoom levels 21 and 22... naturally

[jidanni]

Panning to unexplored areas: the tiles seem to load normally, but why all the errors, particularly around zoom levels 21 and 22?

If I didn't look at the log messages button there on the bottom bar I wouldn't know something was wrong.

Warning Download error: /home/jidanni/.cache/viking/OSM-Mapnik/21/1752674/903328.png
Warning curl_download_uri: http response: 400 for uri http://tile.openstreetmap.org/21/1752674/903328.png
Warning Download error: /home/jidanni/.cache/viking/OSM-Mapnik/21/1752674/903327.png
Warning curl_download_uri: http response: 400 for uri http://tile.openstreetmap.org/21/1752674/903327.png
Warning Download error: /home/jidanni/.cache/viking/OSM-Mapnik/21/1752674/903326.png
Warning curl_download_uri: http response: 400 for uri http://tile.openstreetmap.org/21/1752674/903326.png
Warning Download error: /home/jidanni/.cache/viking/OSM-Mapnik/21/1752673/903328.png
Warning curl_download_uri: http response: 400 for uri http://tile.openstreetmap.org/21/1752673/903328.png

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/400 seems to point the finger at Viking.

[jidanni]

Wait. What makes Viking think that there are more than 19 zoom levels for Mapnik? At least that's how it is on OSM.ORG.
https://www.openstreetmap.org/#map=19/24.181931/120.866100
https://gis.stackexchange.com/questions/174375/loading-tile-zoom-level-20

[rnorris]

The file osm.c contains the OSM Mapnik map definition with a hardcoded limit of zoom-max set to 19.

When panning around it should not (and it does not on my system) make requests for tiles at zoom levels of 20 and 21.

Unfortunately, it appears if you use F5 to refresh - then that bypasses the zoom limit check - and so makes unnecessary/unwanted requests :(

[jidanni]

Also once one somehow gets the half-baked parking lot you see above, one is stuck for life with it. As there is no mechanism to just throw away the tiles one sees, without throwing away more.

Edit: easy workaround: I just went into ~/.cache/Viking and manually deleted the offending files of anything that I wished would refresh.

[jidanni]

But it seems once a tile is in,
the worst thing that could happen is it gets edited upstream,
then we get a permanent mix of old and new tiles.

Oh well, looks like I'll just have to

rm -r .cache/viking/OSM-Mapnik

again.