Making maps requires measuring distances accurately. In the 19th century, before modern air photographs and GPS, ingenious devices known as surveyor's wheels (odometers) were used.
These wheels were usually made of hardwood and were precisely calibrated, with one revolution of the wheel covering an exact distance. In the case of William Logan's odometer, the distance was ten feet, meaning 528 revolutions measured one mile travelled. Generally, these wheels were towed by carriages, with a counting mechanism recording the number of revolutions. Logan, however, simply pushed his odometer along as he moved on foot across the usually rough terrain he traversed.
Because much of the land that Logan studied lacked topographical maps, the odometer was a key part of his task of simultaneously making topographical and geological maps. This was extremely arduous work, but the resulting maps were amazingly accurate using what would now, in these days of GPS, be considered very primitive methods of measurement.
Logan's odometer was on display for many years at the Geological Survey of Canada's museum in Ottawa, and is now part of the Canadian Museum of History's collection.
Logan, W.E., Murray, A., Hunt, T.S., and Billings, E., 1863. Geology of Canada. Report of Progress from its Commencement to 1863; Geological Survey of Canada, 983 p. [accompanied by an Atlas of Maps and Sections.] doi:10.4095/123563
Gray, C., 2004. The Museum Called Canada: 25 Rooms of Wonder; Random House, Canada, 736 p. [see p. 434-439: AND MILES TO GO - Sir William Logan's Odometer.].
Surveyor's Wheel. http://en.wikipedia.org/wiki/Surveyor%27s_wheel