What is the legal basis for an attack upon the validity of a zoning ordinance?

"One permissible basis for an attack upon the validity of a zoning ordinance is that the zoning ordinance is 'spot zoning.' [Citation.] Spot zoning occurs where a small parcel is restricted and given lesser rights than the surrounding property, as where a lot in the center of a business or commercial district is limited to uses for residential purposes thereby creating an 'island' in the middle of a larger area devoted to other uses. [Citation.] Usually spot zoning involves a small parcel of land, the larger the property the more difficult it is to sustain an allegation of spot zoning. [Citations.] Likewise, where the 'spot' is not an island but is connected on some sides to [6 Cal.App.4th 1802] a like zone the allegation of spot zoning is more difficult to establish since lines must be drawn at some point. [Citation.] Even where a small island is created in the midst of less restrictive zoning, the zoning may be upheld where rational reason in the public benefit exists for such a classification. [Citations.]" (Viso v. State of California, supra, 92 Cal.App.3d 15, 22, 154 Cal.Rptr. 580.)