[OSM-talk] Landuse areas etc. abutting highways

Anthony osm at inbox.org
Sun Oct 4 21:47:07 BST 2009


On Sun, Oct 4, 2009 at 4:30 PM, Frederik Ramm <frederik at remote.org> wrote:

> Hi,
>
> MP wrote:
> > b) is easier for editing, more reflecting the reality
>
> I think it is appropriate to choose b) if you indeed have separate
> measurements for each of the three lines, for example a GPS track for
> the road and a land cover import or something.
>
> If, however, you just drove along the road and have *one* GPS track and
> then say "well the road is 10 metres wide so I'll just draw parallel
> lines offset by 5 metres left and right from the centreline", then I'd
> say you are creating artificial detail that has no basis in your data.
> By doing that you make it much harder for someone to later refine your
> mapping. First he'd have to decide whether just because he has more
> precise measurements for the road, does that mean that he should also
> change the nearby areas (unless you have explicitly tagged them
> "source=offset from road centreline" or so).
>

So tag them with a source.  If you're not sure exactly where something is,
you should still make your best guess, not put the location somewhere that
is definitely wrong. I'd rather have people not add information at all than
add information in a location they are sure is wrong.

Pretty much everything you map contains "artificial detail that has no basis
in your data".  The number of decimal places in the node lats and longs is
almost always more than the number of decimal places of guaranteed accuracy
of the source data, whether it's a GPS track, tracing from Yahoo, or
whatever.


> Then, if he decides to also
> refine the field boundaries, he'd have to insert and move nodes in three
> parallel ways rather than just one.


If the boundaries are already there, offset by 5 meters, there wouldn't be
any need to insert nodes, just to move them to the correct offset.

If the way representing the road is being used as the boundary, *then* the
person fixing things would have to insert two new ways, change the relation,
etc. It's a lot easier to fix if the original contributor used method B).
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