Minecraft wiki entry for Old_Customized, associated text: The Minecraft world generator uses many Perlin noise functions to generate the surface terrain. Three Perlin noise functions are combined to form the standard hills: a main function (Main Noise), a lower limit (Lower Limit) and a ceiling (Upper Limit). The world generator is calculated for each coordinate (X, Z) by comparing the average value between the lower limit and upper limit to the value of the main function. The base height (Depth Base) determines the separation between the standard hills and valleys and is independent from sea level.[1]