Another concept if you want true XYZ location with 6" horizontal accuracy and sub-6" vertical accuracy (engineering quality) is aerial mapping. I work for a company that does that so that's my bias. We provide the raw base data by collecting planimetric and terrain (contour) data using photogrammety from aerial stereo imagery. What that means is we'd be able to fly over the trees and use the imagery in a digital stereo software environment to collect a data point at the base of the tree where it sits on the ground. That point would have its own unique ID number and XYZ location. We'd also use the imagery to collect a point field of your whole woods and determine the high's and lo's so you knew which way your sap would flow from any location. Therefore you could locate where to run your mainline exactly by using our raw base data in the GIS package of your choice. As well we could provide orthophotos and overlay that with the vector map data. Print it off or do what you'd like. Technically this is your most accurate means of data collection outside of hiring a surveyor to survey every tree in your woods. Today's gps is getting better but still not as good as aerial photogrammetry. The obvious problem is that aerial mapping isn't cheap, but it's certainly effective especially if your woods doesn't have alot of slope and every percent of grade counts. Here's the shameless plug (link to our company's website.) www.continentalmapping.com