[Tagging] power=* tag: minor_line vs. line

Lauri Kytömaa lkytomaa at gmail.com
Thu Oct 15 10:12:02 UTC 2015


David Marchal wrote:
> I saw conflicting points of view regarding the difference between these two
> ways for modelling aerial power lines: some say that it is the voltage which
> matters, others say that it's the visibility difference that matters, others

Hi.

To properly understand this issue, here's the history of the tags:
- originally, in 2006, there was just the page Key:power (then under the
title "Proposed features/Power Lines") with discussions specifically
agreeing that the project should use a different tag for "large" lines
"strung from latticework pylons" and other lines. At that time, nobody had
seriously thought about ever mapping the smaller ones, and it is a common
separation on all pre-OSM maps (and their source data). Being a global
project, "latticework pylons" referred to the type of construction common in
the countries where the early mappers resided, so even if other countries
used different constructions for high voltage lines, they would still be
power=tower. The original description/proposal
http://wiki.openstreetmap.org/w/index.php?title=Key:power&oldid=6410
and after discussions agreeing:
http://wiki.openstreetmap.org/w/index.php?title=Key:power&oldid=17349#Notes

Power=pole was suggested already in November 2006 for support structures
smaller than power=tower (in the link above)

- in July 2007 the descriptions of power=line and power=tower were copied
to the Map_Features. Still, the assumption and the practice was that people
didn't map "smaller" power lines at all; even if the description of 'line' only
referenced "the path of power cables", it was assumed they'd only be drawn
between power=tower nodes, i.e. only high voltage lines on "big" pylons.
http://wiki.openstreetmap.org/w/index.php?title=Map_Features&diff=39342&oldid=39308

- in January 2008 pages were created for
* Tag:power=tower, with the sentence still present "Should not be used for
electricity or telephone cables carried on single wooden pole."
* Tag:power=line, which still had a description referencing "way following
power cables"
* Key:power was changed to reference the template Map_features:power,
with no change in wording
- In March 2008 some had discussed on the osm talk list that minor
lines could be mapped with a different tag.

- following my question in September 2008 on Talk:Key:power, minor_line was
suggested and others started using it, too, if they hadn't already
prior to that.

- in January 2009 the suggestion to use minor_line for "minor lines with poles
and not towers" was added to the list template, as well as
http://wiki.openstreetmap.org/w/index.php?title=Template:Map_Features:power&diff=next&oldid=206851

- In July 2009 rendering minor_line was already discussed on the talk-de mailing
list.

- in January 2010 the values minor_line and pole were added to the
list template,
after they had proved to be used.
http://wiki.openstreetmap.org/w/index.php?title=Template:Map_Features:power&diff=401683&oldid=344715

In June 2011 some user(s) wrote a proposal to change everything above ground to
'line' and use other tags with an unlimited list of values for
describing their differences.
http://wiki.openstreetmap.org/w/index.php?title=Proposed_features/Power_transmission_refinement&oldid=652518
After discussions and a wiki vote such a change was even rejected in
October 2013,
and the next modified proposal (Power supports refinement) for
redefining power=tower
and power=pole was turned down in May 2015. There is no method in osm to have
the mappers resurvey, reclassify and retag the old data at a whim, nor
a method to
propagate the changes in the contested meaning of tags to (even unknown) data
consumers.

(Digging up these dates I did see a "(overground)" thrown in the
'line' definition to
clarify, but already lost where it was originally. )

In summay, the tags have been used for 9 years as such:
- power=tower: high voltage towers, usually steel latticework
- power=line: overhead lines on strung on high voltage towers
- power=pole: smaller supports, usually one-legged and/or wooden
- power=minor_line: other overhead power lines that don't qualify as power=line
Do note that even if a 'minor_line' has two bigger towers in the
middle, for example to
cross a river or similar, the line as a whole is still minor_line. The
border case of a
remote mapper using the wrong tag for a line or minor line wrongly
identified from aerial
imagery is no different from remote road classification: the local
mappers can and will
correct it later.


-- 
alv



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