Measures of population distribution Variogram: spatial dependence at different spatial scales 1.Take each data value in turn and compute its squared difference from each of the other values in the data set and store the distances between them 2.Group these differences into distance bins – e.g., all squared differences for pairs separated by 1 to 2 km and compute half of the average of these differences 3.Plot these (half) average differences against distances 4.The plot shows how difference between values changes as a function of distance