The properties of soil vary from place to place. The issue is to map the variations. The next question will arise automatically—how to do it? To dig thousands of pits is obviously not economic. The good nature helps us to understand that the variations are not random. “natural soil bodies are the result of climate and living organisms acting on parent material, with topography or local relief exerting a modifying influence and with time required for soil forming processes to act.” This helps us to understand that there is a close relationship between landform and soil.

Soil maps (geopedologic maps) show soil classes (e.g., Podzol with a given set of properties, read also on podzol at Dinkel) and their distribution (e.g., a large area surrounding the city Enschede and the legend). Mapping soils in a given area (with known coordinates) would mean to answer the following questions:

• What are the soil classes, for instance the Podzol (sandy) and heavier textured soils occurring along streams and the river?
  
• Where do they (soil classes) occur (extent/ distribution, for instance in a given area (mapping unit No. 125, 129 on the legend) in the surroundings of Enschede)? Take a wider look to see the other soils (for instance those formed along the river).

How mapping starts?

Mapping starts with landscape stratification (subdividing terrain into meaningful units, on the basis of topography, lithology, etc), by means of image interpretation. Image interpretation takes care of dividing the area (under study) into units, which geopedologically are related to one or more soil classes, depending on the scale (read under  5.5. Geopedologic approach to soilscape analysis, in the lecture-notes image (photo) interpretation). In this way soil surveyor prepares him/ herself to answer the above questions.

Below (Figure 2.1), you'll see the different tools used to carry out image (aerial photograph, Landsat data) interpretation:

Figure 2.1: Image Interpretation

Learn from Video

Stratification (subdivision of terrain into meaningful units)

Once the sites are known, you need to:

• describe the soil profile by characterizing on the basis of which soils can be classified. See also the video describing soil profile.

• and delineate the distribution/ extension, which is to answer a part of the above questions, by means of extrapolation. The extrapolation is done by applying geopedologic approach, where geomorphology and pedology are combined. “Under similar environments in different places, soils are similar. This regularity permits prediction of the location of many different kinds of soil.” This is the backbone concept of the extrapolation.