The number of people living along the U.S. coast is currently 123 million (https://www.natureworldnews.com/articles/1022/20130326/popul...). With a population of more than 327 million people (https://en.wikipedia.org/wiki/United_States), the coast is a bit more than 1/3 but significant less than half and quite far from being majority.

(This is not a comment about calling it urban pockets. 123 millions is a lot. Just a note in regard to the statement that it could be called the majority.)