The Subdivision Act triggers at two parcels
The New Mexico Subdivision Act, NMSA 1978 § 47-6-1 and following, defines a subdivision at § 47-6-2 as the division of a surface area of land into two or more parcels for sale, lease or other conveyance, or for building development, whether immediate or future. Two parcels is the trigger. The Act then sorts divisions into five types by count and size — a type-five subdivision is not more than twenty-four parcels each ten acres or larger, a type-two is twenty-five to four hundred ninety-nine parcels where any one is under ten acres — and review gets heavier as you move up. Counties adopt their own regulations under it, so exemptions and required showings differ county to county.