As you inspect your visualization, make sure you find out what areas on the map have low heads, and what areas have high heads. The main point of this exercise is for you to see how to manipulate color palettes to show the details you need to see in the map. A scalar field like this can certainly be contoured. Unlike a contour map, a color image can also immediately distinguish the highs from the lows on the map, even to the untrained eye. Darker shades appear to the eye to be further away, so are often used to represent low values.
Lighter shades appear closer, and thus higher, to most people.
You may also be familiar with a topographic color palette used on many world maps, where the ocean abyssal depths are deep purple, ocean plains are blue, shallow seas and continental shelves light blue, low plains dark green, uplands light green to yellow, and mountains ascend from orange to white. Add the code to scale the data and write out the raster image. Make sure you are using the same palette as in the first exercise, and are pointing at the Palette Editor. Position the mouse in the upper left of the image. Push and hold the left mouse button.