Cartography Word of the Day: Divide

It’s where water goes one way or the other, one way or the other.

This schematic map of Portland, Oregon (courtesy Cit Of Portland, Bureau of Environmental Services) depicts local water drainages, and the divides that separate them. (Click to enlarge)

When speaking of landforms, the word divide essentially refers to the physical place where one basin is separated from another. Terrain-wise, here we make no distinction between interior basins (with no outlet) and exterior basins (ones which drain to a larger body of water such as an ocean).

The divides everyone is most familiar with are on the continental scale. In North America, this means the Great Divide (the one that runs down the Rocky Mountain contintenal spine) but also the lesser ones: The Northern Divide, which sparates the Arctic Ocean drainage from the Atlantic, as well as the divides that separate out the Saint Lawrence and the Gulf of Mexico drainage from that which goes straight into the Atlantic.

West of the Great Divide, all areas outside the Great Basin (with no drainage outlet) get to the Pacific Ocean or the Gulf of California compratively directly.

Divides also happen on a local level. Every river basin can be subdivided into drainages that collect into local creeks or brooks (or no bodies of water at all). In the illustration above (Courtesy City of Portland, Oregon, Bureau of Environmental Services) the area of the city and some of the immediate surround is depicted in stylized but geographically correct form, with the individual drainages defined. Though the divides are hardly remarkable, and in some areas practically invisible, they are still real and they still govern where water goes.

See also: Wikipedia article on “Continental Divide”