Wikipedia
Spot zoning is the application of zoning to a specific parcel or parcels of land within a larger zoned area when the rezoning is usually at odds with a city's master plan and current zoning restrictions. Spot zoning may be ruled invalid as an "arbitrary, capricious and unreasonable treatment" of a limited parcel of land by a local zoning ordinance. While zoning regulates the land use in whole districts, spot zoning makes unjustified exceptions for a parcel or parcels within a district.
The small size of the parcel is not the sole defining characteristic of a spot zone. Rather, the defining characteristic is the narrowness and unjustified nature of the benefit to the particular property owner, to the detriment of a general land use plan or public goals. The rezoning may provide unjustified special treatment that benefits a particular owner, while undermining the pre-existing rights and uses of adjacent property owners. This would be called an instance of spot zoning. On the other hand, a change in zoning for a small land area may not be a spot zone, if it is consistent with, and furthers the purposes of the general area plan.
For example, a small zone allowing limited commercial uses such as a corner store within a residential area may not be a spot zone, but a carve-out for an industrial use or a night club might be considered a case of spot zoning. In the first case, the differing land uses are mutually compatible and supportive. In the latter case, the residential nature of the area would be harmed by a conflicting land use.
When the change in zoning does not advance a general public purpose in land use, courts may rule certain instances of spot zoning as illegal. The Standard State Zoning Enabling Act states "all such regulations shall be uniform for each class or kind of building throughout each district." It may also be an invalid exercise of authority, if spot zoning is not a right conferred upon the body by the state's zoning enabling statute, because it deviates from the plan set out by the enabling statute.
Special zoning treatment may have a legitimate use, however, such as when a community wishes to have more local control of land use. This may occur in a rural county which has no zoning at all, where a village or hamlet may wish to maintain its characteristic feel and historic appeal (often to protect tourism), without adding another layer of local government and taxes by creating a municipality. The county designates the boundaries (often that of an already census-designated place) and maintain regulations through the county commission instead of a separate town council.