[OSM-dev] MAPNIK - proposal to drop rendering of underground railway lines

Nick Black nickblack1 at gmail.com
Wed May 16 18:03:56 BST 2007

On 5/16/07, Andy Allan <gravitystorm at gmail.com> wrote:
> On 5/16/07, Nick Black <nickblack1 at gmail.com> wrote:
> > To clarify, by underground railways I mean railways that go under the
> > ground.  They cant be seen from the surface and so are not useful for
> > navigation.  Further, I'm not sure if the underground lines in London,
> at
> > least, should even be in OSM as they are just straight lines inbetween
> > stations and don't represent geometry.  The nodes should be in the db,
> but
> > the lines should be inserted by the renderer/editor or whatever client
> is
> > being used.
> I disagree. I looked at central london last weekend and thought "cool!
> The underground lines show up - there's a nice addition that other
> maps don't have". I'm happy to see a distinction made between
> tunnel/not tunnel, but I think both should be rendered anyway.

But what functionality does it add to the map?

It's a bit annoying that whoever put them in didn't make much effort
> to get them right - a lot of the time you can get a fairly accurate
> route for the sub-surface lines from the satellite photos (when they
> go under houses, there's typically a limit to the size of building
> built over the 19th century tunnels - so you can follow where the line
> goes). But I think putting a bit more effort into making them right
> (and look good) would be better than chopping them off of the maps.
> It's worth remembering that the tunnels are physically there, and can
> be mapped to a fair approximation, given a bit of effort.

Maybe for the trench cut, cut and cover tunnels, but you cant possibly map
deep tunnels accurately from optical aerial or satellite imagery.  This
equates to mapping the individual paving slabs on a pavement with a GPS
unit.  The Jubilee line in London has been mapped from space using
interferometric SAR, as the houses directly above it have sunk by severl
milimeters since it was constructed:



Nick Black
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