Biology. equal growth rates in two parts of a developing organism.
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Geography. equality with respect to height above sea level.
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Mathematics. a function from one metric space onto a second metric space having the property that the distance between two points in the first space is equal to the distance between the image points in the second space.
A function between two metric spaces (such as two coordinate systems) which preserves distances. A rotation or translation in a plane is an isometry, since the distances between two points on the plane remain the same after the rotation or translation.