A representation, on a plane surface and at an established scale, of the physical features of a part or whole of the Earth's surface or of any desired surface or subsurface data, by means of signs and symbols, and with the means of orientation indicated. Reservoirs are often represented by a series of maps for each of the layers distinguished within the reservoir. This series of maps may include maps of structure, gross thickness, net thickness, porosity, water saturation and other required petrophysical characteristics. A complete set of petrophysical characteristic maps may constitute a reservoir description, reservoir characterization or reservoir model.