半變異函數顯示測量采樣點的空間自相關。繪制每對位置，然后根據這些位置擬合模型。通常使用某幾個特征來描述這些模型。
變程和基台
查看半變異函數的模型時，您將注意到模型會在特定距離處呈現水平狀態。模型首次呈現水平狀態的距離稱為變程。比該變程近的距離分隔的樣本位置與空間自相關，而距離遠於該變程的樣本位置不與空間自相關。
半變異函數模型在變程處所獲得的值（y 軸上的值）稱為基台。偏基台等於基台減去塊金。
半變異函數示例
塊金
從理論上講，在零間距（步長 = 0）處，半變異函數的值是 0。但是，在極小的間距處，半變異函數通常顯示塊金效應，即值大於 0。例如，如果半變異函數模型在 y 軸上的截距為 2，則塊金為 2。
塊金效應可以歸因於測量誤差或小於采樣間隔距離處的空間變化源（或兩者）。由於測量設備中存在固有誤差，因此會出現測量誤差。自然現象可隨着比例范圍變化而產生空間變化。小於樣本距離的微刻度變化將表現為塊金效應的一部分。收集數據之前，能夠理解空間變化的比例非常重要。
The semivariogram depicts the spatial autocorrelation of the measured sample points. Once each pair of locations is plotted, a model is fit through them. There are certain characteristics that are commonly used to describe these models.
The range and sill
When you look at the model of a semivariogram, you'll notice that at a certain distance, the model levels out. The distance where the model first flattens out is known as the range. Sample locations separated by distances closer than the range are spatially autocorrelated, whereas locations farther apart than the range are not.
The value that the semivariogram model attains at the range (the value on the y-axis) is called the sill. The partial sill is the sill minus the nugget.
Semivariogram example
The nugget
Theoretically, at zero separation distance (lag = 0), the semivariogram value is 0. However, at an infinitesimally small separation distance, the semivariogram often exhibits a nugget effect, which is some value greater than 0. For example, if the semivariogram model intercepts the y-axis at 2, then the nugget is 2.
The nugget effect can be attributed to measurement errors or spatial sources of variation at distances smaller than the sampling interval or both. Measurement error occurs because of the error inherent in measuring devices. Natural phenomena can vary spatially over a range of scales. Variation at microscales smaller than the sampling distances will appear as part of the nugget effect. Before collecting data, it is important to gain some understanding of the scales of spatial variation.