Charge is a fundamental interfacial property that governs physical and chemical interactions at surfaces. The workings of catalysts, sensors, separation devices, biological interfaces, and colloidal systems, are well known to be strongly influenced by surface charge, typically present in the form of protonated or deprotonated chemical moieties. Directly measuring and sensing charge in situ, especially for small (micro/nanoscale), heterogeneous charge distributions presents an interesting and important challenge for electroanalytical chemistry. Here, recent studies in mapping interfacial charge with scanning ion conductance microscopy (SICM) and the influence of electrolyte concentration on the charge sensing mechanism will be described. We have validated a SICM method that utilizes currentvoltage relationships that can be intuitively understood for surface charge detection. The effect of electrical doublelayer (EDL) thickness on signal generation on chemically modified surfaces will be demonstrated. The differential measurement approach used here allows visualization of individual domains of surface charge. EDL effects are modeled with finite element simulations, and extension of our studies to sensing at biological samples and mineral samples will be demonstrated.