Going to try and update throughout the process of creating this next map. Here's where I'm at so far...
Sometimes gradients just don't work very nicely in Illustrator and you end up with the banding you can see in this image. I'll have to play with the colours and layering to get rid of this for the final version.
Like my previous maps, I've kept the lines very straight, using 45 degree angles for bends. I would normally have simplified the edges more, but as Oregon has a mostly rectangular shape doing so would leave it looking pretty bland.
When selecting the buildings I like to use Google Maps street view (where I can. It's a bit harder in Europe). It allows me to wander around the town and act a bit like a tourist. This method also helps force me to break the building shapes down, as street view often has you looking from an angle, not straight on.
Once I've found a good selection, I will start sketching simplified versions of them, usually making them more square, dropping some details and exaggerating others. I don't consider the colours or layouts final until I put them on the map along with all the other objects and see how they interact.
My next step is to lay out the mountain ranges and start making the other assets that will be dotted around the map - animals, unique plants, attractions, etc.