Continents and oceans count as landforms, and so do the smallest slopes
Geographers call a hilltop, a saddle and an entire ocean basin by the same word. A landform is any feature of a solid planetary surface, natural or shaped by people, and the category stretches from a single slope facet to whole continents. Deserts and forests, oddly, do not qualify at all.
The term covers features on the solid face of the Earth or any other planetary body. Hills, canyons, bays and peninsulas belong, and so do things hidden under water, such as mid-ocean ridges and the great basins of the sea floor. Put together, landforms make up terrain, and the way they are arranged across a landscape is called topography. Four types are treated as the major ones on Earth: hills, mountains, plains and plateaus. Basins, buttes, canyons and valleys are ranked as minor.
Classification leans on physical traits: how high a feature sits, how steep it is, which way it faces, how its rock is layered and exposed, and what soil covers it. At the top of the hierarchy stand continents and oceans. Below them, geomorphologists break shapes into named elements such as shoulders, saddles, foreslopes and backslopes, and further down still into elementary units, the smallest patches of ground that look uniform at a chosen resolution. Because a hill or plateau can be studied at anything from a few hundred metres to hundreds of kilometres, what counts as one landform depends heavily on scale.
Several forces build and reshape them. Moving tectonic plates push up hills and mountains, while erosion and deposition wear down and pile up material, sometimes because of human activity. Living things matter too: plants help dunes and salt marshes develop, and corals and algae construct reefs. Some human works are excluded, including canals, ports and many harbours, as are vegetation-defined regions like grasslands.
The vocabulary travels well beyond Earth. Mountains, valleys and polar caps turn up on every terrestrial planet. The field that studies all this is geomorphology, and the proper names of individual peaks and valleys even have their own label, oronyms. Today landforms can be pulled automatically from digital elevation models built from satellite and aerial imagery, with the sharpest models measured by LIDAR, replacing work that once took many costly hours by hand.
Source: Landform
