I don't know if it's already been suggested but the Naples Metro System might work well as a tutorial/ early level to play. It has two lines and twenty stations, though you might need to use some poetic license to connect the two together as they are separate (Mergellina is fairly close to Vanvitelli).
Additionally, the Copenhagen Metro system might work well for the same reason as the Naples Metro. Again it has two lines with twenty two stations. Also those two lines are linked together. They might make for good tutorials (though whether or not the game needs tutorials is another question).