I've created two more maps of rail lines: one for New Hampshire and one for Southern Québec. I find it interesting how different the land-use patterns are between the two areas. Note that I'm working off a variety of old maps, some of which are merely diagrammatic. Thus the exact alignment of some abandoned lines is unknown, and I've certainly left out items.
As a side note, the mapping interface is pretty buggy (at least in my browser). When the number of items on the left side exceeds one page, the list starts doing weird things. The behavior makes sorting the items nicely a real pain in the arse. Hopefully Google will fix this soon.
Update 9/27: I found a very nice repository of old Canadian topo maps, so I'm now pretty confident the routes I've traced are accurate.