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What is a surface plot?
A surface plot visualizes a function of two variables, z = f(x, y), as a height field: for every point on the flat x/y plane the function gives a height z, and connecting those heights forms a smooth mesh floating in 3D. Color usually encodes height, so peaks and valleys stand out at a glance. It is the natural way to picture things like terrain, temperature over a plate, or the shape of a mathematical saddle.