[Tagging] My "weirdly unnatural aversion to relations"

Dave Swarthout daveswarthout at gmail.com
Sun Sep 30 03:54:38 UTC 2018


I'm surprised to learn that a major developer has reservations and concerns
about OSM relations. I don't like them much either. Small ones like simple
riverbanks and lakes containing islands are okay but when they get large,
they're difficult to understand and nearly impossible to debug. There are
myriad tools to "assist" the debugging process but which tool is best to
use and when? And how does the tool itself work? I've got a "polygon is not
closed" error that I must've inadvertently caused on a big riverbank
relation in Alaska. When I go into the relation editor and ask it to "jump
to the error", it highlights an entire, many miles long riverbank. This is
not helpful at all. For the moment I'm stuck. I have much I want to
accomplish in my Mapping Alaska (as I call it) project. Debugging an
obscure error in a large relation slows me down horribly.

I'll be following this thread to see if I can learn more about how to deal
with them.

Dave



On Sun, Sep 30, 2018 at 10:28 AM Joseph Eisenberg <
joseph.eisenberg at gmail.com> wrote:

> Would it be helpful if there were several simpler database primitives for
> several of the simplest types of relations?
>
> I know people have already talked for years about adding a true area
> object (which now we imitate with closed ways)
>
> Could we also have a linear feature made up of ways only? This would
> include the current route and waterway relations. Would something like this
> be helpful, especially if there were a  limit to how many ways could be
> included?
>
> Could multipolygons be specifically defined, perhaps as a type of area?
>
> I do think it is strange that any random collection of nodes and ways can
> form a relation. And the ability to make relations out of other relations
> is also confusing.
>
> But it would be quite helpful to be able to make relations from smaller
> relations, in the simpler cases of a Lake with an island inside
> (multipolygon in a multipolygon), or a long highway made of shorter routes,
> or a long river made of shorter waterway relations.
>
> -Joseph
>
> On Sun, Sep 30, 2018 at 12:01 PM Bryan Housel <bhousel at gmail.com> wrote:
>
>> On Sep 29, 2018, at 6:56 PM, Paul Johnson <baloo at ursamundi.org> wrote:
>>
>> I honestly don't understand why, ten years since it's introduction as
>> OSM's third basic primitive, there's still this weirdly unnatural aversion
>> to relations, even though they're quite a powerful primitive in our toolbox.
>>
>>
>> From my own perspective as the main developer on the main editor for OSM,
>> the reason I don’t like relations very much is because:
>> - every type of node basically works the same.
>> - every type of linear way basically works the same.
>> - every type of polygonal area basically works the same
>> *- every type of relation is an edge case that requires special code in
>> order not to break.  *
>>
>> Relations are also problematic because they are unbounded.  Want to make
>> a boundary relation with a million child ways?  This is allowed.  Want to
>> ensure that all those ways are connected?  It may take minutes to download
>> them all.
>>
>> They’re almost even a security threat.  I’m willing to bet a black hat
>> could design and upload a relation that would destroy OSM.. Or at least,
>> crash every piece of software in the stack that we rely on:  mapnik,
>> osmium, and any editor that tries to touch it.
>>
>> Anyway, I’m not totally against them, but every one of them is different
>> and I can't spend weeks or months supporting every kind of relation or
>> public transport schema people dream up unless it’s super critical for
>> building a useful map (like turn restrictions).  They are really best for
>> features that can not be mapped any other way.
>>
>> Thanks, Bryan
>>
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-- 
Dave Swarthout
Homer, Alaska
Chiang Mai, Thailand
Travel Blog at http://dswarthout.blogspot.com
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