All the arrays of electrodes used to obtain the apparent resistivity are basically superposition of the fundamental equation for the potential from a current source with appropriate sign for the current. The formulas for apparent resistivity are a product of the impedance V/I (Ohms) and a geometric factor with the units of length (meters). To investigate the resistivity distribution with depth, called a sounding, the arrays are expanded about a center point and the apparent resistivities are plotted vs. spacing usually on a log-log plot. In the more general case the apparent resistivities are plotted as a function of array spacing and lateral position using plotting conventions that have become accepted for each type of array.

Pole–Pole
Pole–Dipole
Wenner
Schlumberger
Dipole–Dipole
Hummel