Physiographic regions of the world

The physiographic regions of the world are a means of defining the Earth's landforms into distinct regions, based upon the classic three-tiered approach by Nevin Fenneman in 1916, that further defines landforms into: 1. physiographic divisions; 2. physiographic provinces; and 3. physiographic sections. This foundational model, which Fenneman used to classify the United States, was the basis for similar classifications of other continents later, and is still considered basically valid.

During the early 1900s, the study of regional-scale geomorphology was termed "physiography". Unfortunately, physiography later was considered to be a contraction of "physical" and "geography", and therefore synonymous with physical geography, and the concept became embroiled in controversy surrounding the appropriate concerns of that discipline. Some geomorphologists held to a geological basis for physiography and emphasized a concept of physiographic regions while a conflicting trend among geographers was to equate physiography with "pure morphology," separated from its geological heritage. . In the period following World War II, the emergence of process, climatic, and quantitative studies led to a preference by many Earth scientists for the term "geomorphology" in order to suggest an analytical approach to landscapes rather than a descriptive one. In current usage, physiography still lends itself to confusion as to which meaning is meant, the more specialized "geomorphological" definition or the more encompassing "physical geography" definition. For the remainder of this article, emphasis will remain on the more "geomorphological" usage, which is based upon geological landforms, not on climate, vegetation, or other non-geological criteria.

For the purposes of physiographic mapping, landforms are classified according to both their geologic structures and histories. Distinctions based on geologic age also correspond to physiographic distinctions where the forms are so recent as to be in their first erosion cycle, as is generally the case with sheets of glacial drift. Generally, forms which result from similar histories are characterized by certain similar features, and differences in history result in corresponding differences of form, usually resulting in distinctive features which are obvious to the casual observer, but this is not always the case. A maturely dissected plateau may grade without a break from rugged mountains on the one hand to mildly rolling farm lands on the other. So also, forms which are not classified together may be superficially similar; for example, a young coastal plain and a peneplain. In a large number of cases, the boundary lines are also geologic lines, due to differences in the nature or structure of the underlying rocks.

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