Regardless of the method employed, useful findings uniformly result from contrasts between geophysical measurements acquired over archaeological features and the natural background geology. In other words, if archaeological deposits or features possess physical properties different from the surrounding matrix of measurements, a contrast may be achieved against the normal background in terms of magnetic properties, resistance to an electrical current, or the ability to reflect radar energy.

A buried limestone foundation block might be somewhat less magnetic, more resistant to an electrical current, and better reflect radar energy than the surrounding earth.

Such contrasts are referred to as "anomalies" until they can be identified.

Anomaly identification often requires archaeological excavation.

Frequently, anomalies can illustrate pattern sufficient for their identification. as when the rectangle of a house foundation is clearly expressed.

Anomaly identification becomes easier as the experience base grows in a region.

Rarely is a single geophysical measurement important. Many observations are necessary to determine normal background levels and to locate differences, or anomalies, from the smoothly varying background.

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