Horsham is one of the original townships laid out, but not named, on the first published map of William Penn’s settlement in Pennsylvania. This map, commonly known as Holme’s Map, was printed during the year 1687 by Penn’s London land office, from reports submitted before the end of the previous year by his Land Commissioners, resident in Philadelphia, and by Thomas Holme, his Surveyor General for the Colony. Holme used a simple method of blocking out land in the east end of Montgomery and Bucks Counties. He ran parallel lines northwestward from the Delaware River at intervals of one and one-half miles; each alternate line established division line between townships; the intervening lines formed median or base lines within the townships, from which individual grants of land were measured. Horsham forms one of a tier of townships set apart in this manner, and extending from the Philadelphia county line through Hatfield Township. Similar tiers flank these townships both to the left and to the right.

Through highways were projected along each of these parallel lines. When actually laid out, these highways occasionally deviated somewhat from the straight lines of the survey, due to irregularities of terrain, but in a general way. most of the southeast-northwest roads in the eastern end of Montgomery County and the adjacent section of Bucks County follow the old survey lines laid down more than 250 years ago. Township Line Road or Cottman Street, Susquehanna Road, Welsh Road. Horsham Road, County Line Road, Street Road, and Bristol Road all follow closely the basic lines found on Holme’s Map.