<P> The elevation at a point or unit of terrain will have perpendicular tangents (slope) passing through the point, in an east - west and north - south direction . These two tangents give two components, ∂ z / ∂ x and ∂ z / ∂ y, which then be used to determine the overall direction of slope, and the aspect of the slope . The gradient is defined as a vector quantity with components equal to the partial derivatives of the surface in the x and y directions . </P> <P> The calculation of the overall 3x3 grid slope S and aspect A for methods that determine east - west and north - south component use the following formulas respectively: </P> <P> tan ⁡ S = (∂ z ∂ x) 2 + (∂ z ∂ y) 2 (\ displaystyle \ tan S = (\ sqrt (\ left ((\ frac (\ partial z) (\ partial x)) \ right) ^ (2) + \ left ((\ frac (\ partial z) (\ partial y)) \ right) ^ (2)))) </P> <P> tan ⁡ A = ((− ∂ z ∂ y) (∂ z ∂ x)) (\ displaystyle \ tan A = \ left ((\ frac (\ left ((\ frac (- \ partial z) (\ partial y)) \ right)) (\ left ((\ frac (\ partial z) (\ partial x)) \ right))) \ right)) </P>

Which of the following is the most complete and accurate definition of information technology