They have two maps - why, I don't know. If you ask for a map, they'll tear one off a tablet and give it to you - it's about 13 by 18 1/2 inches, and the type is so small as to be not terribly useful. They have a larger version (already folded) which is 18 1/2 by 26 inches. Much easier to read! But you may have to insist to get them to give you this one.
The last time I was in Rome, even though I speak Italian and asked for the larger map, they tried to tell me it was the same as the smaller one. Then they tried to tell me they only had it in Japanese! So keep insisting!
And of course, every guide book on earth has a map or series of maps. The cut-away maps of small neighborhoods in the Eyewitness Guide are great - but the book weighs a ton!
Still, my favorite is the Rough Guide's Map of Rome. Just detailed enough to keep you from losing your way in the tiny vincoli (alleys) that make the city so enjoyable. And made out of that wonderful, untearable, waterproof fabric that allows you to fold it again and again, in any way you like, in any way that's convenient for your current location. I love it.
Whatever map you choose - do this one little check. Look for Piazza Paradiso. Find Piazza Venezia (just north of the Roman Forum and Piazza Campidoglio). Then follow Corso Vittorio Emanuele to the west until you come to the Church of San Andrea delle Valle (which should be on the south side of the street.)
Ok, now find Campo dei Fiori, just to the southwest, and draw a line between it and the church. If you don't find Piazza del Paradiso just about in the middle, then the map isn?t detailed enough.Actually, maybe it's getting lost and not caring one bit!

