A region perceived to exist by its inhabitants is a

Perceptual  region

Explanation:

A perceptual or vernacular region is defined by feelings and prejudices that may or may not be true I believe:)

a mid-ocean ridge or mid-oceanic ridge is an underwater mountain range, formed by plate tectonics. this uplifting of the ocean floor occurs when convection currents rise in the mantle beneath the oceanic crust and create magma where two tectonic plates meet at a divergent boundary.a geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged.

answerpeople organize large projects such as levee-building;