Well EPCOT i think has the world largest parking lot, but its right there in front of the park. And each spot is a very quick walk to the tram station, and the ride maybe takes 50 seconds, to 1 minute. AK has the parking lot in front, and MGM has the parking lot in front as well. But MK's parking lot is in front but further away from the park. It has a lake in between MK and the parking lot, and you just take a ferry boat over the lake to the park, or you can take the monorail. There are two lines, the resort line, or the epcot line. The resort line goes to five of the resorts, and then to MK, and the epcot line goes from the MK parking lot to Epcot. There is a station right in front of the MK, but you have to go through a few resorts, so its easiest to just take the five or ten minute ferry boat.
Just go to
www.maps.google.com and search Walt Disney world followed by the park name. Epcot or Magic Kingdom, and then click satalite, and you'll see what it all looks like.
It looks like it'd be very confusing going from one park to another, and there is a pretty elaborate road system, but once you drive into any of the road entrances to Disneyworl (you'll know cuz there is a huge arch with WDW on it) then you'll see all sorts of signs guiding you to the different parks.