Of course --
First, your Via 1535 came with 4GB of internal memory. For a while, that was enough to hold the entire North American map. However, they keep adding roads, parking lots, speed limits etc and it starts to add up. It's no longer possible to fit the whole thing into the 4GB of internal memory.
Next, understand that your map has to fit all in 'one place', either internal or external. So if it won't fit in internal in 4GB (most of which is the map), trying to stuff it onto a 2GB external uSD card isn't going to happen.
You have two choices. If you try to continue with your installation given your current enviroment, MyDrive Connect will eventually suggest that you download some portion (there are several options) of the North American map. However, if you'll just stick a nice 8GB Class 10 (larger or faster will be overkill, but may be cheaper on Black Friday) uSD card into your 1535, you'll find that the entire North American map will fit. That's why the slot was provided.