Landforms are divided into 11 major categories: Aeolian, coastal and oceanic, erosion, fluvial, impact, karst, lacustrine, mountain and glacial, slope, tectonic and volcanic. Within these groupings are many landform subtypes.
A landform is a part of the Earth's surface that exists naturally, meaning it is not human-made. This makes all natural terrain landforms of one type or another. The type of landforms common to an area are dictated by global geo-history, weather conditions and other factors. Hills, mountains, gulches and bayous are all landforms. The four hierarchical layers of landforms are oceans and continents, landform elements, terrain and elementary landforms.
Oceans and continents are the largest and highest-order landforms. Landform elements are features of these high-order landforms that can be more distinctly labeled as discrete elements, such as the tops and shoulders of hills. Terrain is a vertical description of surface landforms, while elementary landforms are the smallest possible divisions of a landform that can be observed discretely.
Human-made terrain features, such as artificial ports, canals and artificial lakes, are not landforms. The terminology of landform study and observation is not confined to Earth systems sciences and can readily be applied to the topography of other planets in and outside the solar system. This makes it an important component of space exploration and astronomy.