A look-up table is defined by at least one reference point, and rows and columns that are offset from the reference. The table rows and columns correspond to ordinate and abscissa data points representing geographic locations. Each data point offset in the table corresponds to a predefined geographic offset. The look-up table contains machine-stored values at each table location, with each value representing a particular one of several guidance zones. Each guidance zone is associated with behavioral guidance provided to an animal Real-time determination of a current guidance zone is made by first determining present location. The corresponding table location is identified by calculating latitudinal and longitudinal offsets from a reference point, and using these offsets as the two indices to access a double-indexed array. The offsets are selectively subjected to a scalar conversion to accommodate large land areas while limiting the amount of memory required to store the table.