"Roland Perry" wrote

I think the City branch of the Northern Line goes west of Mornington
Crescent. And if the Northern and Victoria have a cross-platform change
at Euston (I forget if it's true) then they shouldn't really be shown
crossing at right angles!

Victoria Line and City branch of the Northern Line do have cross-platform
interchange at Euston. As you would expect, the cross-platform interchange
is between the northbound Victoria and northbound Northern Lines, and again
between southbound Victoria and southbound Northern Lines, though curiously
Victoria and Northern trains run in opposite directions through the station.
If you want to travel from Euston to Kings Cross (allowing for the walks to
and from the surface it's probably quicker to walk on the surface then whole
way) you take either a northbound Victoria Line, or a southbound Northern
Line, train.

Peter