On 17 April 2012 02:50, Alan Mintz <[email protected]> wrote:Technically, everything is a polygon, since a line cannot exist in the physical world.
- At 2012-04-16 11:46, Sam Kuper wrote:
- On 16 April 2012 02:15, Serge Wroclawski <[email protected]> wrote:
- On Sun, Apr 15, 2012 at 8:57 PM, James Ewen <[email protected]> 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 areà polygons, not lines) as polygons is a bug in dire need of fixing.Â
Boundaries are lines.
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- 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.
For OSM map purposes, why? It's the center of the road right-of-way. Nothing is implied other than that. If one wants to get the center of each traffic direction, the road can be split into dual-carriageways, which is often done. Individual lanes could be done, too, but there is no widespread support (demand) for that level of detail. You can probably find some examples where people have played with it, though.
- 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?
Designing, building, and mapping roads. Civil engineers and GIS professionals.
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?
- 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.
http://gis.dpw.lacounty.gov/landrecords/index.cfm is an interactive map of Los Angeles county's docs. Zoom in and you'll start to see colored polygons that represent pages of various types of docs. Click on them to list them on the left and click on the links there to see the PDFs. AFAIK, they've digitized everything they had. Some of the docs are quite interesting, historically.
 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?
Yes, if you really need/want such information and have support for creating and maintaining it, there's nothing to stop you from serving a mash-up of your data with whatever you need from OSM.
Alan Mintz <[email protected]>
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