Officially it's to help "customers living with claustrophobia or anxiety conditions who find it difficult using the Tube" "by showing them routes they can take to avoid areas with large stretches of tunnels." A wholly laudable aim.
But some of the 'tunnels' are a bit short, barely even 100m in length, which isn't much worse than going under a bridge. I wonder if the map will deter some people from using stretches of line they previously wouldn't have worried about.
'Tunnels' less than 100m in length
Dalston Kingsland - Hackney Central (30m)
Leytonstone - Snaresbrook (40m)
Clapham Junction - Wandsworth Road (40m and 70m)
Walthamstow Central - Wood Street (50m)
Either side of Denmark Hill (50m and 80m)
Crouch Hill - Harringay Green Lanes (60m)
Westbourne Park - Royal Oak (70m)
Highbury & Islington - Canonbury (80m) (how many more can we find?)
(I'm using Open Street Map to estimate distances)
At least one of the 'tunnels' doesn't actually exist.
'Tunnels' which shouldn't appear on the map
Shadwell - Tower Gateway (there are no tunnels on this branch) (how many more can we find?)
Also, if we're being pure about this, there are other places where tracks go underground (in at least one direction) which aren't shown.
'Tunnels' missing from the map
Kew Gardens - Richmond (40m)
Harrow-on-the-Hill - West Harrow (40m)
Kingsbury - Wembley Park (50m)
Upney - Barking (westbound) (60m)
Lewisham - Elverson Road (60m)
Cyprus - Gallions Reach (80m)
Gallions Reach - Beckton (100m)
Croxley Curve (because that's not on the map) (how many can we find?)
Unofficially, obviously, the new map is to tell people whether they'll be able to get a phone signal or not.