We describe a simple way to compute the response of an irregular resistive interface to a Laplacian field in d = 2. It permits to find the linear response of electrodes with an arbitrary geometry from the image only of the electrode. It also allows to compute the non-linear response of self similar electrodes. This method applies in principle to arbitrary irregular geometry in d = 2 and it permits to predict generally that the slope of the Tafel plot is divided by the fractal dimension.