Contextual districts were created in 1987 in conjunction with the Quality Housing Program in NYC as an amendment to the 1961 Zoning Resolution. They came about as a response to out-of-scale development in residential areas where height-factor buildings were breaking up the aesthetic cohesion of older neighborhoods across NYC. Contextual districts offer floor area ratio (FAR) advantages that non-contextual districts do not receive. They are also subject to maximum base heights, building heights, and street-wall regulations in order to maintain the conformity of the streetscape. (nyc.gov)
There are two main types of contextual districts: Low Density and Medium-High Density. Both types are identified on zoning maps with the suffixes A, B, X or 1, and attached to the standard residential zoning codes R1-R10, where R1 is the lowest density neighborhood and R10 is the highest.
Low Density contextual districts (R2X, R3A, R4-1, R4A, R4B, R5B) include detached, semi-detached, and row house neighborhoods typically found in Queens, the Bronx, Brooklyn and Staten Island. In these districts, limitations on curb cuts maximize on-street parking and promote traditionally landscaped front yards.
Medium-High density contextual districts (R6B, R7A, R7X, R8A, R8B, R8X, R9A, R9X, R10A) require buildings that are at or near the street line, and offer maximum floor area ratios for buildings regardless of height factor regulations or open-space ratios. The heights of the buildings in these districts are set by sky exposure planes, where a building may not obstruct sunlight at street level. (nyc.gov)