[Tagging] Relations (was directions)

Serge Wroclawski emacsen at gmail.com
Tue Aug 9 15:44:05 BST 2011

On Tue, Aug 9, 2011 at 10:11 AM, Ilya Zverev <zverik at textual.ru> wrote:

> Of course. When you get to the road you'll see its surface and lane count,

Lane count and surface are useful for many things:

For routing, for rendering, for analyzing traffic and capacity.

Tell me what direction is useful for other than 3d rendering.

> OSM offers many
> perspectives. From the perspective of routing the direction of road sign is
> important.


> From the perspective of 3D rendering physical attributes and
> rotation are important. OSM has stopped being just a map the moment someone
> specified building levels count.

OSM isn't a 3d representation of the earth. It's a 2d representation,
and a rough one at that.

>> The problem with a direction tag is that then suddenly every object
>> has a direction relation, and we make editing the map far more
>> complex.
> "The problem with a name attribute is that then suddenly every object has a
> name tag, and we make editing the map far more complex." This is not a
> proposal's problem, but with relations in general, I guess?


Relations are a solution that should only be used as a last resort.
They cause many many problems. We have to use them but before we do we
should ask ourselves:

1. Is this data representable some other way? Through tagging for example?

2. What is the relationship I'm building my relation on? A relation
describes relationships. What are my objects and their role to each

3. Is this something people will find useful other than me?

4. How would I code support for this? Since relations are complex,
maybe spend some time in the PL2/Josm code and think about how you'd
build a UI for it, and maybe think about how a renderer would support
it, not just in theory but in practice.

> Should we reduce their count to
> mininum, creating alternative ways to map turn restrictions, destination
> signs, surveillance cameras, public transport routes?


Relations are overused in OSM, and it causes a huge amount of
difficulty in spreading mapping.

I am often editing relations that other people make; they're often
broken. They're broken because it's hard to make them correctly, and
fixing a relation isn't easy- you have to break the objects apart,
check their roles, check their construction, and reassemble the

Relations make the map hard to work with.

Let's take your example. Let's say I find a road need to be split and
fixed because of construction. Now I have to worry about the relations
on that road, and check each and every segment that's created.

I'll tell you that many mappers won't do that, which means that the
relations won't be right. What's left is bad data. It's like an
abandoned wiki.

The more I fix other's data, the more clear these problems appear.

- Serge

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