Valley, elongate depression of the Earth's surface. Valleys are most commonly drained by rivers and may occur in a relatively flat plain or between ranges of hills or mountains. Those valleys produced by tectonic action are called rift valleys. Very narrow, deep valleys of similar appearance are called gorges.
Spatial competition occurs when the amount of space available is inadequate to satisfy existing or expected future wants. For example space for transport or agriculture may be at the expense of space for ecosystems
