One of the references seems to have a little more detail, and also some leads for more learning: http://www.pbs.org/wayfinders/wayfinding2.html http://www.pbs.

One of the references seems to have a little more detail, and also some leads for more learning: http://www.pbs.org/wayfinders/wayfinding2.html http://www.pbs.org/wayfinders/wayfinding2.html