Introduction

Every graph we have seen so far in this book has been a plot of one quantity versus another quantity, or in the case of parametric plots, two coordinates that depend on a single third parameter. These are called two dimensional (2D) plots. In this chapter, we break into the third dimension. The graphs here are visualizations of quantities that depend on two variables; they are expressed as surfaces, contours, fields of arrows, paths in space, or as a combination of these elements.