All settings regarding texture mapping are located on this page.
Enable Texture Mapping specifies whether to use textures at all. If disabled, the scene is rendered with gouraud shading by default.
Texture Edge Length controls how the texture is scaled against the map. Setting this parameter to 1 means that the texture is mapped to exactly one square in the heightmap. Setting this parameter to the width of the heightmap means that the texture is applied to the whole heightmap. This behaviour can also be achieved by setting Texture Edge Length to zero.