# How to Calculate a Semivariogram ••• Imgorthand/E+/GettyImages
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A semivariogram is a mathematical function that shows spatial correlation between measurements of samples and are often represented graphically. Semivariograms are usually covered in advanced spatial statistics courses. One application of semivariograms is to calculate the average value of iron at different drilling locations.

Draw a grid, where "h" represents the distance between samples. A 100 feet x 100 feet grid, advocated by geostatistical researcher Dr. Isobel Clark, allows you to visualize the problem and perform easier calculations.

Write the value for the sample at each intersection.

Find every pair of measurements that are 100 feet apart horizontally.

Square the difference in value between each pair.

Add up all of the squares and divide the answer by 2(number of pairs). This answer is a graph point.

Repeat Steps 3 to 5 for 200 feet, 300 feet, 400 feet, 500 feet and 600 feet (stopping at about half the total sample size).

Plot on a graph with distance between samples (feet) on the x-axis and experimental semivariogram (the numbers you calculated above) on the y-axis.

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