It's a tough question to give a simple answer to, because you are dealing with two different things - mapsets and routes.
As you already know, mapsets are stored on the data card. Routes are stored in a reserved area of memory within the GPSR itself. What will likely happen, in the circumstance you describe, is this: You'll load the first data card with the mapsets that comprise the beginning of your route, then activate your route. All will look just fine (excepting a message you will get when you activate the route, advising you that you don't have all the necessary cartography) until you run off the mapset that you have loaded.
At that point, you will need to switch data cards, and then tell the GPSR to recalculate the route. Most likely, it will pick up where the new mapset begins, and present you with suitable guidance.
A far simpler way of handling the matter is to create two routes - in other words, just break your existing route in half at about the point where the mapsets break in half. Load one 'duplicate' map segment onto both data cards, to allow for guidance during the overlap. Then, load the first data card, and activate the first route. When you see that you are getting into the boundary area (the duplicate segment that marks the middle of the route), just change data cards, and activate the second half of the route. Doing things that way is a heck of a lot simpler, and you can be assured you will not have problems with accurate guidance over the transition between data cards.
Michael
