A method for displaying contour maps of two-dimensional functions is described. The function is first recorded in a computer-generated hologram (CGH). Then the moire formed between the CGH and a regular grating creates a contour map of the function. This method allows the number of contours in the moiré to be increased even after the CGH is made. An example illustrates some interesting results when this method is used to display the equipotential lines or the lines of force of an electrical dipole in a uniform electric field.