[OSM-talk] [OSM-newbies] layers in OSM?

[Zeke Farwell]

Replying to a Newbies thread, but beyond the scope of that list so I moved
here.

I've been thinking about layers for a while.  In OSM we do not use layers
for different types of features as one would in traditional GIS.  I suppose
the benefit of this is simplicity, but in very dense areas, things can get
very cluttered and hard to edit.

One result of data overload seems to be that mappers want to minimize
duplication (I include myself in this group).  If there is a case where two
areas overlap on one side, we convert them to multipolygons that share a way
where they overlap.  This is good.  But how about when an administrative
boundary is directly on top of a highway or a river for miles and miles?
 The nodes blink at you in Potlatch.  Surely two ways are unnecessary and
one way shared by a relation for the boundary and a relation for the
highway/river would be better, no?  There has been lots of discussion about
if and when it is correct or not correct to do this.  I have flipped back
and forth on this question, but lately it has occurred to me that the use of
layers could nullify the whole debate.  If layers were built into the OSM
data structure, administrative boundaries could have their own layer.
 Layers would not be able to share objects, so the question of highways and
boundaries sharing ways would not come up.  If a boundary happened to
exactly follow a road, one could simply copy the way from the highway layer
to the boundary layer and change the tags.  Later if someone wanted to edit
the road but not the boundary it would be quite easy to select the road by
simply turning off the boundary layer and vice versa.

Clearly too many layers could make OSM far too complicated.  Here are two
that I see a real benefit to having though:

   - Physical - everything that is verifiable by going somewhere and looking
   around.
   - Non-Physical - administrative boundaries, nebulous place names, landuse
   (not land cover which is physical).  Basically things that can only truly be
   verified by laws & treaties (national boundaries), or things that are not
   well defined but clearly agreed upon (Most people know where the Alps are,
   but there is no exact boundary)

I see a benefit to these being separate because a non-physical feature can
be defined by a physical feature, but that does not make it the same as the
physical feature.  Take the boundary of a forrest and the boundary of a
field for example.  As more trees grow, the forrest expands and the field
shrinks.  The boundaries for these two physical features are one and the
same.  Now take the boundary of a township, county, or state that is defined
by a river.  As the river changes course over time, the boundary of said
political entity may or may not change depending on how the law is written.
 Though they may coincide, the two are not inexorably linked as the boundary
of a field and a forrest are.

Let me qualify this post by saying that I participate in this project only
as a mapper and I have no knowledge of how the underlying database or API
works.  There are probably many technical challenges and/or reasons not to
do this that I haven't though of.  I am simply tossing out some food for
thought.  Also this may have been discussed at length before and put to
rest.  If so I apologize for bringing up dead topic.  I'd be interested to
know what was said though.

Zeke


--
Zeke Farwell
Burlington, VT, USA




On Sat, Sep 4, 2010 at 9:46 AM, Eric Jarvies <eric at csl.com.mx> wrote:

>
> On Sep 4, 2010, at 6:57 AM, Serge Wroclawski wrote:
>
> > On Sat, Sep 4, 2010 at 7:15 AM, Xan
> >
> >> But, why don't you integrate the layers in OSM web page? Now we could
> choose
> >> Mapnik, Osmarender, ... why not put another possibility: "choose layer".
> >> Yeah!, I know it's a littble bit work (!) to do but it could be cool!.
> Very
> >> cool and (I think) useful....
> >>
> >> Perhaps in talk-devel? ;-)
> >
> > Xan,
> >
> > You're right that this probably beyond the scope of the newbies list,
> > but let me ask you a question:
> >
> > What is your use case?
> >
> > If your use case is that what you want is a rendered layer for
> > displaying as a base map, that's a different matter then, say, wanting
> > a "layer" to be converted into a Shapefile and then imported into
> > another tool, and is yet distinct from "I just want to look at one
> > attribute in order to edit it" and is still yet distinct from "This
> > would be really cool".
>
> Having both would be nice.  Being able to render raster tiles of each
> individual layer would be nice... as it would be nice to 'easily' output
> .osm(or .shp, etc.) files by key:value selections.
>
> Eric Jarvies
>
> >
> > These are each different and I'd handle them differently, so knowing
> > what you're looking for will help all of us answer the question (even
> > if we stay on this list to do it).
> >
> > - Serge
> >
> > _______________________________________________
> > newbies mailing list
> > newbies at openstreetmap.org
> > http://lists.openstreetmap.org/listinfo/newbies
> >
>
>
> _______________________________________________
> newbies mailing list
> newbies at openstreetmap.org
> http://lists.openstreetmap.org/listinfo/newbies
>
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