From The Art and Popular Culture Encyclopedia
Region is most commonly a geographical term that is used in various ways among the different branches of geography. In general, a region may be seen as a collection of smaller units (as in "the New England states") or as one part of a larger whole (as in "the New England region of the United States"). Regions can be defined by physical characteristics, human characteristics, and functional characteristics. As a way of describing spatial areas, the concept of regions is important and widely used among the many branches of geography, each of which can describe areas in regional terms. For example, ecoregion is a term used in environmental geography, cultural region in cultural geography, bioregion in biogeography, and so on. The field of geography that studies regions themselves is called regional geography.
In the fields of physical geography, ecology, biogeography, zoogeography, and environmental geography, regions tend to be based on natural features such as ecosystems or biotopes, biomes, drainage basins, mountain ranges, soil types.