The regulation of land subdivision and building was based principally on precedent, practice and custom rather than a codified set of legal principles and regulations. In Edo, different sets of regulations applied to daimyo, hatamoto and townsmen, and to different status levels within each class. Mizuno proposes an extensive and detailed classification system for analytical purposes which encompasses all aspects of the regulation of the construction industry in the Edo Period. Architectural regulation beyond the external and public expression of social position was a complex and less concise matter. Regulations issued by the Okayama-han in 1668 restricted walling to notsuratsumi construction and placed limitations on the type of boarding to be used on the lower external walls of enclosed structures. Internal walls and associated fittings were also subject to regulation, but were unaffected by fire requirements which related only to the external surfaces of the building.