Non‐technical summary  Axons are long process of nerve cells that mediate communication and control within the organism. Mammalian neurons have developed a complex ion channel clustering mechanism in axons to optimize rapid signalling. It has been discovered recently that intricate details of the spatial pattern of channel clustering play a critical role in signal processing in the axon. The electrical properties of axons, however, have been difficult to study using electrodes because axons are very small in diameter. We took advantage of a critical methodological improvement in the high sensitivity membrane potential imaging (V_m imaging) technique to study electrical correlates of channel clustering in the axon of cortical neurons. Voltage imaging revealed the location and length of the axonal site for nerve impulse initiation as well as the pattern of saltatory conduction in myelinated axons in the form of dynamic spatial maps of transmembrane potential.