Which terrain feature is classified as a linear feature that can be an obstacle to movement?

A river is classified as a linear feature that serves as an obstacle to movement due to its continuous nature and the inherent difficulties it presents when trying to cross or navigate alongside it. Rivers can create physical challenges such as needing to find a suitable crossing point or dealing with the potential for swift currents. This characteristic makes rivers significant considerations in tactical planning, as they can significantly impede the movement of personnel and vehicles.

In contrast, hills, valleys, and forests, while they may also affect movement, do not possess the same linear quality as rivers. Hills can vary in shape and may provide advantageous or hindering elevation changes but do not create a continuous barrier like a river does. Valleys often provide a route for movement, and while they can be restrictive, they do not function as a linear obstacle. Forests can complicate movement due to density and visibility issues, but they do not create an impassable linear boundary in the same way that a river does.