[OSM-talk] The Return of the Highway tags and other junk

[Dirk-Lüder Kreie]

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Ben Robbins schrieb:
> 
>> I have several issues with the current tagging system, nevertheless I
>> use it to the existing standard, because at the moment I cannot come up
>> with something better.
> 
> I'm trying to have a debate on the creation of something better for a
> few tags (features/borders), and the creation of a new, none replacement
> tag, for other things.  My proposals are better to the extent that
> without doing this way somethings don't work at all, but Im shore there
> is better yet, and am awaiting suggesions.
> 
>> Nodes are mathematical points, segments are mathematical lines, so
>> technically these are all incorrect. However there is some default space
>> usage assumed, depending on the attributes of the node/segment/way.
>> So if you tag a node "cattle grid" it should be clear that the cattle
>> grid is a non-dimensional thing but something that will span the entire
>> width of the road at that point and occupy some length of the road as
>> well. The Method of data gathering of OSM is not accurate enough to
>> warrant a mapped area for something as small as a cattle grid. Or a gate
>> for that matter.
> 
> I ment that gates and cattlegrids are a line, so therefore a segment, as
> drawing them as very narrow rectangles is unessesery.

And I say it's even not necessary to draw them as a line, because you
can deduct the relevant dimensions from the surroundings and the tags.

> For acuracy of placement the reasons against adding it acuratly are no
> reason that drawing it as an adjecent line is better than drawing it as
> a node.  There both placed realtvie to gps data and notes.
> 
> Just as a building may be a node if it hasnt been acurately mapped yet,
> a cattlegrid may be a node, but I think it should when posible be moved
> up to a line.   Just as a street is ok without a name, but when the name
> is found it should be added.

A building doesn't need to be accurately mapped, unless it has some
significance (even by size alone) and/or perhaps a recognizable shape.

>> Remember that a map is always a simplified model of the world, you have
>> to leave out insignificant information for example the exact dimensions
>> of a cattle grid or gate, that only matters if it limits traffic, by
>> means of maximum weight, width and/or height.
> 
> There are 3 reasons I add gates in this way, and there not so that the
> exact dimensions can be seen.
> 
> 1) So that it is clear what gate you are looking for when walking.  It
> may be a footgate, or a double gate, or a gate adjacent to the direction
> your walking.

The latter should be obvious from the context the gate-node is put in,
the former can be set by tags (even if you draw it as a segment, so
that's no argument for using a segment for a gate)

> 2) So that the gate can lie along the hedge.  If a gate is a node, then
> 2 gates would be nodes? then why not make a short hedge a node, or a
> long hedge...when do long thin feature start becoming segments?

~10m in my opinion, unless relevant for topology, even larger if
irrelevant, like we don't render each house on a residential road it's
just not relevant. You can add the numbers (to a segment like: 3-9,2-10)
if you somehow need to identify the amount of houses in a street.
I'm not sure what you mean by "2 gates": as in there are 2 "wings" to
one gate? No, that's still only one node, and maybe, just maybe a tag to
that effect.

> 3) They render better with no more rules than a line colour and
> thickness.  Cattle grids require a few layers of rendering but are still
> easy to render.

Layers? I don't understand why a cattle grid would need layers. One icon
maybe rotated to align with the road and fence.

> Leaving out the insignificant information is different to having a tag
> that stops the insignicant infomation being added.  What is
> insignificant is debateable.  But as you said, it only matter if it
> limits traffic.  If true then a gate and cattle grid do just this, as
> they decrease speed, and access.

I still don't understand why a gate that's less than, say, 10 m wide
needs to be tagged as a linear thing.

We are creating maps. Maps are abstracted from the real world. I
understand that we are currently debating the level of abstraction. In
my opinion everything you try to achive by adding these complex entities
can be achieved by a reasonably connected and tagged node.
And like Andy Allan said, if someone else has to update your data, he
won't know why you placed your nodes the way they are and will probably
unknowingly destroy what you have fine-tuned.

Dirk-Lüder "Deelkar" Kreie
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