I have a record dated from the Hunterdon County Orphans' Court dated May 4, 1797, excerpted from "More Records of Old Hunterdon County, Volume I" compiled by Phyllis D'Autrechy and edited by Roxanne K. Carkhuff, pub. Hunterdon County HS, Flemington, NJ, 1998, that discusses partitioning the land of John Emley between his brothers and sisters and their heirs.
The "White Hall Farm" was one of these pieces of land.Evidently, the heirs of Elizabeth Mott (sister) received Lot 1, Elisha Emley's heirs got lot 2, and William Emley's heirs got lot 3.Lot 3 was bordered by "Lots 1&2, lands in possession of John Leonard, land in possession of William Osmun, the south side of the Great Road to Pitts Town".Today Pittstown is at the junction of Rts. 579 and 513.I don't know if one of these was the "Great Road" they mention, but it's possible.
I'm researching the Osmun / Osman families in NJ and was curious to know whether or not the map you were looking at listed the Wm. Osmun above near the Emley land.