N.Y. Comp. Codes R. & Regs. tit. 16, § 255.5 – Class locations.

(a) Except as provided in paragraphs (d)(2) and (e)(2) of this section, the class location is determined by the number of buildings intended for human occupancy in the class location unit. The class location unit is an area that extends 220 yards (201.17 meters) on either side of the centerline of any continuous one-mile (1.61 kilometers) length of pipeline. For the purposes of this section, each separate dwelling unit in a multiple dwelling building is counted as a separate building intended for human occupancy.
(b) A Class 1 location is any class location unit that has 10 or fewer buildings intended for human occupancy.
(c) A Class 2 location is any class location unit that has more than 10 but fewer than 46 buildings intended for human occupancy.
(d) A Class 3 location is:
1. (1) any class location unit that has 46 or more buildings intended for human occupancy; or
2. (2) any area where the pipeline lies within 100 yards (91.44 meters) of either a building or a small, well defined outside area that is occupied by 20 or more persons during normal use (such as a playground, recreation area, outdoor theater, or other place of public assembly).
(e) A Class 4 location is:
1. (1) any class location unit that has 100 or more buildings intended for human occupancy and where wall to wall pavement is prevalent; or
2. (2) any class location unit where buildings with four or more stories aboveground are prevalent.
(f) The boundaries of the class location unit determined in accordance with subdivisions (a) through (e) of this section may be extended according to the following.
1. (1) When a cluster of buildings intended for human occupancy otherwise requires a Class 2, 3 or 4 location, the class location unit ends 220 yards (201.17 meters) from the nearest building in the cluster.
2. (2) When the number of buildings with four or more stories requires a Class 4 location, the class location unit ends 220 yards (201.17 meters) from the nearest building with four or more stories.