Preparing maps before an adventure takes time. Another method is to make the scenery up on the fly during the game, jot it down as you go, and have that become the map of the region the PCs are in. The disadvantages being that you have to be on the ball the whole time, and it's easy to forget some detail that the players will want to come back to later.

Because you can bet your life that the one thing you forget to record will be the one thing they start obsessing over. Even more so since you'll suddenly be stumbling over the fact that it may or may not exist, thus only serving to increase the players' suspicion that it must be important.

Transcript

GM: Right, I think it's a good time for a break.
GM: If you want to keep asking random NPCs for maps of areas between interesting places, I'll need some time.
Leia: Sorry.
GM: No no, it's cool. My well of improvisation is just starting to run dry.
R2-D2: But at least it's a new and exciting adventure for all of us!
C-3PO: Pete, with all this publicity, I've been thinking of organising a march at the university.
R2-D2: Good. Keep it orderly, and register with the police beforehand. You want to get noticed, but don't piss people off. Leave the path to the coffee shop clear.
C-3PO: Annie, can I show your video?
Leia: Of course.
Chewbacca: You should invite someone to make a speech. A famous ape scientist, perhaps.
Han: Yeah! Like Dr Zaius!
{beat}
Chewbacca: Your wisdom walks hand in hand with your idiocy.