The easiest way to look at the Disney bus system is to consider each theme park and DTD as a mini-hub. So if you are at a resort (let's say, All Star) and you want to get to another resort (let's say WL), travel from your resort to the mini-hub closest your destination (in this case, MK) and then transfer at the hub to transportation to your destination.
The important thing is to pay attention to park hours. For example, if you have a dinner reservation at Boma, you may be dining later than AK is open. If you aren't going to be able to make a connection at the closest park, DTD is usually your best alternative, as they have transport until at least 1:00 am.
With the new bus dispatch system, I doubt if they will be publishing much in the way of route maps anymore, as any bus can be sent anywhere at any time. It's always a good idea to confirm with the drive as you enter the bus that it's going where you need to go.