I was raised in Northern NJ, lived in Baltimore, and now reside in Coastal South Carolina. I went to a NY style deli the other day and ordered an Italian sub. Now, I should have known better but I didn't even think to ask if the sub came with mayo. Sure enough after 1 bite, I came away with a mouthful of mayo. (It's an Italian sub - it should not be hot and should not have mayo but that is another post.) I was thoroughly disgusted that my lunch had been ruined.
What did happen was that I started thinking about where this magical line lies that divides the land where mayo is a sometimes condiment and the land where it becomes not only a prerequisite but a main ingredient. Everything on this certain Deli's menu had mayo, even the egg sandwiches. I'd say that the line lies somewhere in southern Maryland. I guess that makes Maryland a mayo border state. Is it the further South that you go the more prevalent mayo usage becomes? So if I go to Miami will I just get a mayo on rye? How about travelling west? Anyway, thought that you chowhounds might have some input