[Talk-GB] mapping tunnels

Michael Collinson mike at ayeltd.biz
Fri Sep 28 08:39:45 BST 2007

At 12:19 AM 9/28/2007, Thom Shannon wrote:
>Does anyone have any suggestions how to map a long tunnel? I know how to
>tag the ways, the issue is where does the tunnel go. You can't exactly
>get a GPS trace! I want to map the tunnels under the Mersey. The
>queensway tunnel has 3 exits, all at slightly odd angles and there is a
>junction in the middle of the tunnel.
>Do you think I could figure out some reasonable positions using a cars
>odometer and a compass? Or does it not really matter that much?
>Another option just occurred, the tunnel was started in 1925, so any
>maps from that era would be out of copyright. Perhaps a trip to the

I feel that completeness of main features is more important than 
accuracy in these early days of OSM.  I therefore simply join the 
tunnel mouths with as few nodes as possible (so that no one gets the 
idea I have a mysterious source of information) and mark the tunnel 
way source=interpolation.  I sometimes place minimum nodes between 
the tunnel mouths if there is an obvious curve and if there are 
internal junctions on a best effort basis.

Of course in the longer term better accuracy would be good, 
out-of-copyright maps would be your best bet I think.  From 
experience in my UK home town, you may also find a local history 
museum or historian with a town planning map from the twenties - the 
features may, of course, not have been built or may have been 
adjusted but such maps were more widely distributed than actual 
engineering plans.

[and Otley - Centre of the Known & Unknown Universe] 

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