SYNONYMS Variogram modeling DEFINITION The first law of geography states that "Everything is related to everything else, but near things are more related than distant things." For example, it is natural that nearby places have similar climate as compared to places which are far apart. Amount of rainfall and iron ore deposits vary gradually over space. Such natural processes that vary gradually with respect to distance are said to be spatially correlated. A semivariogram is one of the

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... functions to indicate spatial correlation in observations measured at sample locations. It is commonly represented as a graph that shows the difference in measure and the distance between all pairs of sampled locations. Such a graph is helpful to build a mathematical model that describes the variability of the measure with location. Modeling of relationship among sample locations to indicate the variability of the measure with a distance of separation between all sampled locations is called semivariogram modeling. In addition to summarizing the variation in measurements with distance, semivariogram modeling is also used as a prediction tool to estimate the value of a measure at a new location. Semivariogram modeling is applied in fields related to spatial data, such as ecology -to study the vegetation cover, meteorology -to study the variation of climatic effects such as rainfall, geology -to study the distribution of minerals such as iron ore and predict the iron ore content at a known location, etc.