[OSM-dev] Very long ways have been split (was: Status of Database Server after 0.4 Upgrade: Fragile)

Frederik Ramm 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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