San Ysidro is a district of the City of San Diego, immediately north of the U.S.-Mexico border. It neighbors Otay Mesa West to the north, Otay Mesa to the east, and Nestor and the Tijuana River Valley to the west; together these communities form South San Diego, a pene-exclave of the City of San Diego, thus making it possible to travel (by water) between central San Diego and South San Diego without ever leaving the city limits. Major thoroughfares include Beyer Boulevard and San Ysidro Boulevard.