There is adopted the official zoning map of the city and all property within the city is placed in the zones as indicated on said map. A copy of the map shall be maintained in the city offices by the city clerk and duly certified by him. All amendments to the official zoning map shall be noted thereon with the date of the amendment and references to the amending ordinance. The official zoning map is made a part of this chapter the same as though set forth at length in this section.

All land or territory annexed to the city after the effective date of this title shall be immediately classified to permit the same uses permitted in the territory by the zoning ordinance and map of Los Angeles County, and only such uses. The zone classifications shall have the same designation as existed while the territory was unincorporated territory, except that the letters "LAC" will follow the zone designations and be a part of the designations. The council may establish specific zoning by ordinance for land or territory to be annexed. Such an ordinance may be adopted concurrently with the annexation. Unless such specific zoning is established by ordinance, the zoning map shall be amended so as to indicate the land or territory annexed as having the zone designations as prior to annexation plus the symbols "LAC," provided however, that the territory within Northerly Annexation No. 1 shall be in those zones as indicated on the official zoning map adopted in Section 18.16.020.

Notwithstanding the provisions of Section 18.16.030, all land or territory annexed to the city after the effective date of the amendment codified in this section which is classified under the zoning ordinance of the county with a minimum area requirement of one acre or more may be used for those purposes permitted under the zone classification R-A-20,000 under the city zoning ordinance, and the zoning map shall be amended so as to indicate such land or territory as having such zoning designation.

Whenever any map in this chapter, whether added thereto before or after the effective date of this section, shows any lot or area within any particular zone, such zone shall extend to the center of every adjoining road or highway, provided that while such road or highway remains a public highway or a road used in a similar manner it may be so used.

If a zone boundary so divides a lot that either or both portions of such lot created by the division are not in zone B-1 or B-2, and of such size and shape that no part of such portion is more than fifty feet from the zone boundary, then that portion or portions not in zones B-1 or B-2, and of such size and shape that no part of such portion is more than fifty feet from such zone boundary may be used for any purpose permitted in the other portion of the lot is: