Minecraft wiki entry for Old_Customized, associated text: There are 16 customization options that can be used to affect various aspects of Minecraft's terrain generator. These settings appear on two pages: one with sliders, and one that allows for text input. On the manual text input page, typing in any value lower or higher than the allowed parameter changes the value to the lowest or highest value possible for that customization option. The settings change only the mountains and valleys of the landscape; structures and other environmental factors (which are set on page 1) remain unaffected.