Final answer:
The smallest subdivision affected by the Subdivision Map Act is a quarter-quarter section, or 40 acres. This land division system originates from the Northwest Ordinances, with townships being the basic unit subdivided into smaller sections.
Step-by-step explanation:
The smallest subdivision affected by the Subdivision Map Act is a subdivision comprising quarter-quarter sections of forty acres. When referring to the subdivisions related to the grid system established by the Northwest Ordinances, a township is the basic unit, spanning six square miles. Each township is divided into 36 sections, each section equating to 640 acres, which can be further divided into quarter sections (160 acres) and then into quarter-quarter sections (40 acres). These subdivisions facilitated the sale and settlement of land in the United States.
The Subdivision Map Act is a legal framework that governs the division of land, and the smallest parcel scale that is commonly acknowledged in land transactions, under this framework, is the quarter-quarter section. This geometric pattern of land division, defined in the Ordinance of 1785 and later the Ordinance of 1787, is still visible in the American landscape today and has played a significant role in land development and management.