A method for automatic contouring of two-dimensional geophysical data is presented in this paper. The method is based on piecewise bicubic spline representation of uniformlygridded data points derived from irregularly-spaced observations. The testing of this method has been carried out with a set of data digitized along flight lines at points of intersection with contour lines on a published aeromagnetic map. The map is conspicuous by the presence of steep gradient as well as broad, smoothly-varying regions. A critical examination of the machine-contoured map with respect to the published hand-drawn map establishes the accuracy and reliability of the automatic contouring program. In this paper a short account of bicubic splines is followed by a description of the contouring program, the input data required by the program, and the results.