[OSM-talk] Very long ways

Dirk-Lüder Kreie osm-list at deelkar.net
Wed Mar 28 13:08:05 BST 2007

Hash: SHA1

Mike Collinson schrieb:
> At 02:17 PM 28/03/2007, Lars Aronsson wrote:
>> Are there any guidelines for how long ways should be?  Either by number of segments or by geographic size? > 

> More generally from my editing rather than rendering or technical db
> point of view:
> Number of segments:  Probably irrelevant?   The more, the slower it
> is to download.  If they are in your current edit area, you still
> need to download them whether it is one or several ways. If they
> extend outside your area, it is pointless to download them but the
> crucial factor is the geographic size, not the number.

I agree, the segment count is only a measure how painful it will be to
download the way if it's incomplete.

> Geographic size:  The bigger, the more statistically likely the way
> will be incomplete in any given edit and cause problems.  
> I came up with 12km for long distance features such as railways and
> 1.5km for urban ways.

I thought about this as well and came up with a very similar number.

> 1.5km seems good but 12km too small for countries like Canada and
> Australia.  Doubling the allowed OSM download area would give 24km,
> which might allow a way break at the next turn-off or bridge and
> would allow for less crowded labelling on 1:250,000 and 1:500,000
> maps.

There is no problem when creating the way to create it as one long, 1500
km (or whatever length) way, tag it and then splitting it up.
(preferably before upload)

> Rationale:
> I'd should say the rough guide is about half the geographic width of
> the JOSM window when you do your initial download (a sort of Nyquist
> frequency).
> At the moment OSM won't let me download if the slider is set to over
> 2.1 km, so that gives me 24 km of window so 12km optimum length.

the api restricts the bounding box an area equivalent to 0.3*0.3
degrees. This means you can, if you have a looong east-west road in
Australia perhaps, manually edit the bbox for the request to be 0.01*9
degrees in size.

> When dealing with 500km roads I find that a pain in the behind.
> Allowing double the download window for working in sparsely populated
> areas of the world would allow 24km, not great but workable.

As stated above, create the way in one long piece, then split at
bridges, onramps or whatever.

> I'd say 24km max and preferably half that, 12km, would be good in
> sparsely populated areas and for long distance features such as
> railways and motorways.  24 km is roughly the width of a JOSM screen
> when the slide bar is set to 2.1km, the maximum that you can download
> from OSM at them moment.
> For dense urban areas where your edits are probably going to be very
> local and you don't want to download the whole city,  I tend to
> download with the JOSM slider set to 263m --> 3km window --> 1.5km
> way length.

For motorways (which are the roads in Germany that run the real
distances) I split them at every "important" exit outside, and at
*every* exit inside urban areas, resulting in something like 10-40 km
outside and 2-5 km inside urban areas.
(The former is not really optimal, but given the low node density on
motorways due to their not-too-curvy layout, still manageable.)

Dirk-Lüder "Deelkar" Kreie

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