[OSM-talk] Mapnik tileset coherency issues

[Patrick Weber]

Hi list

These comments are from a total newcomer to OSM, so please if this issue 
has been beaten to death before, ignore me.

Mapnik's tileset gets updated once a week on Wednesday's, is that right? 
I wondered how long the update of the whole tileset takes, as I can see 
now on Thursday morning, that depending on the zoom level,  changes are 
included, and when zooming in, they disappear again. Also, between tile 
boundaries, changes might appear and thus new roads get cut off.
Now I believe this can be a bit disconcerting for casual browsers of 
OSM, that dont understand the whole updating process going on behind the 
scenes, and "might" make them think less of OSM's data quality than it 
really is.

As I see it, Mapnik is the "production" tileset, the official face of 
OSM, versus OsmaRender T at H is for map editors who want to check their 
updates and people wanting the latest data. My point is then, that 
Mapnik should be an attempt to present a coherent view of the OSM data. 
Thats where I think the updating artefacts become an issue.

Now, as I understand it, only tiles marked "dirty" get rerendered and 
immediately replace old versions in the live tileset.
Could there be a mecanism to render these tiles without committing them 
immediately to the live tileset, saving them in a cache, and only when 
all dirty tiles have been rendered, to update the tileset in one go by 
replacing tiles in the live tileset? Would that solve coherency issues I 
just explained? Would there be enough space on the server to keep while 
rendering thus dual copies of "dirty" tiles ?

Please let me know if I am completely off with my ideas

Patrick

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