Concepts and basic methods for extracting notional, formal and effective emission areas are considered. A functional dependence of the notional emission area on the field is obtained, taking into account the shape of the emitter. An analysis of the current-voltage characteristics in semi-logarithmic coordinates ln(I/Uk) vs 1/U, called “k-power plot”, is proposed, which makes it possible to take into account the shape of the emitter, to linearize the dependence, and, therefore, to obtain effective values of the field enhancement independent of the voltage range.