Can someone explain the boundaries of Gibraltar?

Gibraltar is a British Overseas Territory located on the southern end of the Iberian Peninsula at the entrance of the Mediterranean. It has an area of 2.6 square miles and a northern border with the Province of Cadiz in Andalusia, Spain. The Rock of Gibraltar is the only landmark in the region. At its foot is the densely populated city area, home to almost 30,000 Gibraltarians and other nationalities.