Broke - sorry - I misunderstood your question - I thought you were asking about basic horn styles of the period rather that types of maps horns.
The map horns that I have seen are associated with military campaigns, roads or forts. I have seen a lot of contemporary map horns that people make of areas they are interested in or live in, and I am not saying they did not exist in the 1700s, but the original map horns I've seen are associated with the military campaigns, roads and forts, sometimes made there, sometimes made as commerative horns. So you have the Hudson and Mohwawk Valley horns, "Forbes Road" horns, the Grant Expedition horn that documents a campaign against the Cherokee, the Fort Pitt, Fort Edward, Ticonderoga, Crown Point horns, etc.
So for 1779-ish, map horn in that area, I could see a horn showing the New York area forts or campaigns of 1776, or perhaps some of the New Jersey area battles from the intervening period. Or a Mohawk Valley horn (Oriskany, Fort Stanwix etc.).
Or maybe a map of Sullivan's campaign against the Iroquois towns in 1779 - upper Mohawk valley and upper Susquehanna headwaters regions - something akin to the Grant Expedition/Cherokee horn. I've not seen a Sullivan Campaign horn, but I would not be surprised if some were made.
Here is some info on Sullivan's Campaign and a period map of the campaign you can enlarge. Apparently, there were troops from New Jersey, New York, Pennslvania, Virginia and the New England states and a lot of involvement by riflemen. The campaign had profound consequences for the Iroquois.
http://www.earlyamerica.com/review/1998/sullivan.htmlhttp://sullivanclinton.com/maps/images/iroquoisinvasion.jpgGood luck
Guy