Maps in art - any issues?

Lots of artists use maps in their art - are there copyright issues involved?

I'd like to print my "journey lines" onto big maps of the Underground, but using actual maps seems to have two main issues:

1. getting hold of the maps

2. copyright - the London Transport Museum website says:

"The Underground map and logo, New Johnston font and the London Transport Museum poster and photograph collections are protected by copyright"

Ah well, back to looking at other artists' use of maps - for instance these six, and this blog about maps, a book I have (somewhere) and an essay by its author, links to the use of maps in the blogosphere, oh so much more....

Finally a picture -

Imperial Quilt by Susan Stockwell. There's more to see on her website...