When locating Thoreau’s surveys, begin by comparing the current GIS 2010 Concord map with Gleason’s 1906 Concord map, F. W. Beers’ 1875 Concord Map, and Walling’s 1852 Concord Map below.
current GIS 2010 Concord map
Note the Hawthorne Lane Bridge correctly located.
http://www.mapsonline.net/concord/
Gleason’s 1906 Concord map
Walling’s 1852 Concord Map
Thoreau’s Chronological Atlas 