chula vista and imperial beach are cities in san diego counties....san ysidro, nestor, otay mesa are all communities in san diego...just look at the police dept. imperial beach gots sheriffs....and chula vista got the cvpd....san ysidro gots sdpd............................ALSO THERE IS TWO BORDERS, OTAY MESA AND SAN YSIDRO...........WHICH ONE IS THE BORDER TOWN????? its san diego county.....