For purposes of Government Code section 56375.3, an “island” is an area of unincorporated territory that is (1) completely surrounded, or substantially surrounded—that is, surrounded to a large degree, or in the main—either by the city to which annexation is proposed or by the city and a county boundary or the Pacific Ocean, or (2) completely surrounded by the city to which annexation is proposed and adjacent cities. An “island” may not be a part of another island that is surrounded or substantially surrounded in this same manner.