So let's set up the scenario. I depart KOXB and I am flying a 270° heading as required on departure. This lets Patuxent ID me and then they will turn me on course. We'll assume we are flying along fat dumb and happy, direct ENO and eventually handed off to Dover approach. Dover is the controlling ATC between Ocean City and Wilmington.
Once completed I select MAP and confirm I am on course to SIE.