where z denotes a data value at a particular location, h is the distance between data values, and n(h) are the number of pairs of data values a distance of h apart.
A plot of the semivariance versus distance between data values is known as a semivariogram[?], or simply as a variogram[?].
... Morton Stanley, (1841-1904), found back Livingstone; later explored Lake Victoria, Lake Tanganyika and the Congo River
William Stairs, (1863-1892), Victorian explorer, ...