Digital Mapping of Soil Classes and Continuous Soil Properties

Soil is often described as mantling the land more or less continuously with the exception being where there is bare rock and ice (Webster and Oliver 2006). Our understanding of soil variation in any region is usually based on only a small number of observations made in the field. Across the spatial domain of the region of interest, predictions of the spatial distribution of soil properties are made at unobserved locations based on the properties of the small number of soil observations. There are two principal approaches for making predictions of soil at unobserved locations. The first approach subdivides the soil coverage into discrete spatial units within which the soils conform to the characteristics of a class in some soil classification (Heuvelink and Webster 2001). The second approach treats soils as a suite of continuous variables and attempts to describe the way these variables vary across the landscape (Heuvelink and Webster 2001). The second approach is necessarily quantitative, as it requires numerical methods for interpolation between the locations of actual soil observations.