1. A method of characterizing subsurface conditions in a selected geographic region previously associated as a whole with a specific subsurface material characteristic reference profile, the method comprising deploying a sensing tool at a selected position within the geographic region, the tool constructed to be responsive to a selected subsurface material attribute; determining, from a signal received from the deployed tool, a depth-referenced subsurface material characteristic at the selected position; comparing the determined subsurface material characteristic to the subsurface material characteristic reference profile associated with the geographic region to determine a correlation between the subsurface material characteristic reference profile and the depth-referenced subsurface material characteristic as determined from the signal received from the deployed tool; and then deciding whether to deploy the tool at another position within said geographic region by considering the correlation determined from said selected position.