An order establishing a district as a subsidiary district may be adopted if upon the date of that order the commission determines that either of the following situations exists:
(a) The entire territory of the district is included within the boundaries of a city.
(b) A portion or portions of the territory of the district are included within the boundaries of a city and that portion or portions meet both of the following requirements:
(1) Represent 70 percent or more of the area of land within the district, as determined by reference to the statements and the maps or plats filed pursuant to Chapter 8 (commencing with Section 54900) of Division 2 of Title 5 for the current fiscal year.
(2) Contain 70 percent or more of the number of registered voters who reside within the district as shown on the voters’ register in the office of the county clerk or registrar of voters.