[Tagging] length=

[Yann Kacenelen]

Hi Mike, hi François, hi all,
 
I don't find the "length=*" tag redundant either for linear objects
like streetlines, especially in the case of pretty steep ones: as
they're projected for mapping purposes from 3D to 2D, their actual
length is not the one you measure on the map but you should consider
dividing it by cosinus(A) where A is the angle of inclination between
the local horizontal plan and the linear feature. Pythagore said it, man
;-)
E.g.: a 17-degree mapped mountain road or San Francisco street's will
get its actual length a 5% bonus compared to its real-life counterpart.
Pick a 100-meter-or-more road, it's not just a bunch of cm. Depends on
the accuracy you need, mostly for analysis purposes.
 
http://en.wikipedia.org/wiki/Grade_%28slope%29
http://www.datapointed.net/visualizations/maps/san-francisco/streets-slope/
 
My 2c,
 
- Yann


>>> tagging-request at openstreetmap.org> 27/01/2015 16:15 >>
( mailto:tagging-request at openstreetmap.org) 
Date: Tue, 27 Jan 2015 16:13:17 +0100
From: François Lacombe <fl.infosreseaux at gmail.com>
To: "Tag discussion, strategy and related tools"
	<tagging at openstreetmap.org>
Subject: Re: [Tagging] length=
Message-ID:
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Hi Mike,

I don't find it redundant since the length=* tag can give the real
length
of a feature.
The way in OSM is only a (sometimes not precise) drawing of an
existing
feature and can be different from the reality.

The wiki can be completed with such a nuance.

I personally recommend to use the length key while mapping street
cabinets
as nodes.
http://wiki.openstreetmap.org/wiki/Tag:man_made%3Dstreet_cabinet

All the best

*François Lacombe*

fl dot infosreseaux At gmail dot com
www.infos-reseaux.com
@InfosReseaux <http://www.twitter.com/InfosReseaux>

2015-01-27 16:04 GMT+01:00 Mike Thompson <miketho16 at gmail.com>:

> I have noticed a "length" tag used on some linear ways [1]. It seems
> that this is redundant, as the length could be calculated from the
> geometry itself.  It could also be the source of future errors
should
> someone split the way, for example to add more detailed tagging,
such
> as varying smoothness.
>
> The length key does have a wiki page [2], but the page doesn't have
> much content.  Perhaps it is only intended for nodes?
>
> What do you think?  Should the length tag be used with ways and
> relations where the length can be calculated from the geometry
itself?
> Am I missing something?
>
> MIke
>
> [1] https://www.openstreetmap.org/way/324078614
> [2] http://wiki.openstreetmap.org/wiki/Key:length
>
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