(

a) The general plan shall be so prepared that all or individual elements of it may be adopted by the legislative body, and so that it may be adopted by the legislative body for all or part of the territory of the county or city and any other territory outside its boundaries that in its judgment bears relation to its planning. The general plan may be adopted in any format deemed appropriate or convenient by the legislative body, including the combining of elements. The legislative body may adopt all or part of a plan of another public agency in satisfaction of all or part of the requirements of

Section if the plan of the other public agency is sufficiently detailed and its contents are appropriate, as determined by the legislative body, for the adopting city or county. (

b) The general plan may be adopted as a single document or as a group of documents relating to subjects or geographic segments of the planning area. (

c) The general plan shall address each of the elements specified in

Section to the extent that the subject of the element exists in the planning area. The degree of specificity and level of detail of the discussion of each element shall reflect local conditions and circumstances. However, this

section shall not affect the requirements of subdivision (

c) of

Section 65302, nor be construed to expand or limit the authority of the Department of Housing and Community Development to review housing elements pursuant to

Section of this code or

Section of the Health and Safety Code. The requirements of this

section shall apply to charter cities.