Devices, systems, and techniques include determining spatial relationships between electrodes implanted within a patient. In one example, a medical device delivers, via a first electrode, an electrical stimulus and senses, for each other electrode, a respective electrical signal indicative of the electrical stimulus. The medical device determines, for each other electrode, a respective value for each respective electrical signal. The medical device determines, based on the respective values for each respective electrical signal and values of tissue conductivity of tissues of the patient interposed between the first electrode and the other electrodes, spatial relationships between the first electrode and each other electrode of the plurality of electrodes.