[OSM-newbies] How to draw land-use areas

[Sam Kuper]

On 17 April 2012 02:50, Alan Mintz <Alan_Mintz+OSM at earthlink.net> wrote:

> At 2012-04-16 11:46, Sam Kuper wrote:
>
> On 16 April 2012 02:15, Serge Wroclawski <emacsen at gmail.com> wrote:
> On Sun, Apr 15, 2012 at 8:57 PM, James Ewen <ve6srv at gmail.com> wrote:
>
> > My personal feeling is that if you're going to map landuse to the >
> physical edge of the road, then you should create the road as a > polygon
> to show the edge of the road sharing the edge of the landuse.
>
> Roads as polygons is really poorly supported in OSM, and by poorly supported,
> I mean that for the most part, they're not at all, and should be avoided.
>
> While you might be able to render them, the renderer already has support
> for rendering road size based on road type- using areas will mess that
> up. In addition, AFAIK, none of the routing engines in OSM support roads
> as areas, so using them would be a problem for both renderers and routers.
> In my view, OSM's lack of support for roads (which are polygons, not
> lines) as polygons is a bug in dire need of fixing.
>
> Technically, everything is a polygon, since a line cannot exist in the
> physical world.


Boundaries are lines.


> So, proper tools (including OSM) either add a width property to them or
> assume a width based on other criteria (like road class). This works fine
> for most purposes, and avoids the performance penalties of unnecessary
> detail.


I don't think it works fine at all. Lots of sections of road aren't
symmetrical, for a start. Centreline plus width strikes me as misleading in
these cases.


Map roads as polygons, I say! And any of us finds that the tools don't
> facilitate that, then (s)he should stop tagging for the moment and turn
> her/his attention to improving the tools.
>
> If we get this right, then eventually we'll be able to use OSM to look up
> the dimensions of roads, pavements, traffic islands, central reservations,
> etc, which has the potential to be very useful in support of open planning.
>
>
> I disagree. Even professionals see no need for this.


Professionals at which aspects of which professions?


> County road databases (all that I've seen) are all based on centerlines,
> with traffic classes, widths, etc. well-used for necessary traffic
> planning. The details of particular curb, lane, and island placements are
> all available in the various map books, which are often available online by
> links.


I'd be genuinely interested to see examples showing how to correlate the
data from such country road databases and map books. Please could you
provide some?


> This isn't because of lack of capability - all current tools have support
> for polygons - it's simply a matter of using the right feature for the job.
> There's no reason to overload one map layer with all that detail that is of
> no importance to the vast majority of consumers.
>

Are you proposing that OSM should use one layer for roads as lines, and
another layer for roads as polygons?


> In the OSM world, I believe it's not presumptive to say that the vast
> majority of mappers are unwilling to go out there with a survey crew and
> measure the type of details your talking about, nor to (probably manually)
> import them from engineering drawings, nor to want to support the
> performance penalty caused by having to render all that detail,


Not yet. Give it time.


> for no real benefit to them or anyone they can think of.
>

Yet :-)

Sam
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