In the scene where Ewan McGregor drives to Belmont MA to visit Paul Emmett, he checks the mailbox to see who mail is addressed to. It shows the name Paul Emmett, address, Belmont MA 02324, which is the wrong zip code; it is the zipcode for Bridgewater MA, and Belmont MA should be 02478.
McGregor finds that the BMW navigation system is active, and decides to follow the directions, having no idea where it will lead. There are obviously much easier and direct ways to check the entered target destination of a sat nav than actually following it. Instead of this being a mistake, it is most likely a script choice; portraying McGregor as stressed, technically unknowing, inexperienced driver of modern luxury cars, or all of that.