gradient

Qualities vary, slowly, subtly, gradually, across the extent of each thing. Gradients occur (p 205). …(they) will follow as the natural response to any changing circumstance in space, as centers become adapted correctly to the changes which move across space: in doing so, they will vary systematically, thus forming gradients (p 206).

Measure slope between two occurrences with different elevations (p. 92)

 As magnitudes vary over the extent of a distribution then the slope or gradient between adjacent points increases or decreases. Gradients also depend on the distances apart of the occurrences. Peaks of concentration and pits of scarcity emerge from transforming the two-dimensional point locations into a three-dimensional continuous surface in which the representation of gradients or slopes become completely dependent on the interpolation criteria chosen (p. 38)

Change in the value of a variable in spatial coordinates. A field is the rate of change of a variable with distance from a reference point or surface. The rate (slope) may be more or less ‘steep’ by analogy with topography. The oceanic ‘thermocline’ is the rapid fall off in temperature with depth below the uniformly mixed layer at the surface. Physiological processes often depend on the maintenance of ionic gradients, e.g. in nerve tissue, the kidneys, the mitochondrial membrane, chloroplasts, etc.