[OSM-dev] Very long ways have been split (was: Status of Database Server after 0.4 Upgrade: Fragile)
frederik at remote.org
Sun May 13 22:50:00 BST 2007
>> Are they going to render correctly if you've split the ways, so they
>> don't form closed ways anymore?
> More importantly (to me), why are we systematically destroying data to
> fit into some arbitrary tool? These lakes are now no more recognizable
> as polygon areas, but instead two linestrings. Great, now we can't pick
> out polygons anymore automatically, instead we have to manually
> postprocess the data.
The API is not "some arbitrary tool". Even if it *could* handle ways of
any length (which it cannot) there would have to be some sort of cutoff
point; the whole Eurasian coastline may be a polygon, and it may be
"destroying" data to split it into several parts, but it is simply not
practical to have it as one way. (Whenever a download bounding box
contained a bit of coastline, you'd have to download hundreds of
megabytes of coastline!)
So it is obvious that we need a mechanism to deal with large areas
*without* having them in the data base as one single polygon. This is
not something under discussion, it is a fact.
The coastline display in tiles at home is solved; I don't know how Mapnik
deals with it but Mapnik cannot reasonably expect us to have one way for
the whole coastline of a continent. Other areas do not yet render
properly in tiles at home if they're not a closed way, but a solution to
that is around the corner (with a modified close-areas.pl); I cannot
speak for Mapnik but I don't see a big computational problem in
reconstructing an area from joined ways if you need it.
I could have split only things larger than 1000 segments or larger than
1500 segments or whatever, but given we need to find a proper solution
for the problem anyway, why should we stretch the limit?
I am able to undo the splitting of all or of selected items on the list
and restore areas to being closed ways, but I really don't see the point
- we cannot have closed areas for everything that logically is one
entity, so why fight over individual cases?
Frederik Ramm ## eMail frederik at remote.org ## N49°00.09' E008°23.33'
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