The following sections look at visualization of scalar values over points forming a rectilinear grid (gridded) and scattered 2D point sets, as illustrated in Figure 14.1. These data could represent locations over which elevations are known. Or, the data could represent the number of units sold for two toy products over which the profit will be plotted. Perhaps we have a function such as f(x, y) = sin(xy), that we want to visualize.