I will discuss how scanning tunneling potentiometry (STP) and Kelvin probe force microscopy (KPFM) can be used to quantify and image the electrochemical profile of graphene/hBN devices biased with in-plane currents. It will be shown how these measurements can reveal the profiles of in-plane electrostatic potentials of devices with and without a current bias. I will then demonstrate how the scanned probe tip can be used to draw electrostatic barriers in the device which act to locally perturb the current flowing through the graphene sheet. STP measurements of the current profile around circular barriers and through constrictions reveals that at low temperatures the flow is ballistic, but as the temperature is raised it becomes viscous due to a phase transition of the charge carriers in the graphene. In the viscous regime, interesting features in the flow can be observed including greater-than-ballistic conductance through narrow channels, and Landaur residual resistivity dipoles with reduced magnitude.