The analyst may also qualitatively describe the erosional or depositional landforms of an area. As discussed in
Lesson 2, once the landforms have been identified, the types of materials most likely comprising them may be
determined. For example, a point bar is generally composed of sand- to gravel-sized particles, whereas a
floodplain consists mainly of clay- and silt-sized material.
5. Analysis of Vegetation. Although climate strongly controls the overall vegetation of a particular region, the
chemistry and structure of a soil, as well as its moisture content, also exert an influence on the type of vegetation
encountered. In a given climate, if only one type of vegetation is dominant, the underlying soil is probably
homogeneous. On the other hand, if the vegetation prevailing in one area can be distinguished from that of
another, the two areas are probably underlain by different soil types. As a photo-interpretive key, vegetation is
employed mainly as a rough guide to indicate the broad variability of soil types within a specific region.
In addition, the type of vegetation present in an area may also be used as a crude indication of the underlying soil
type. For example, deciduous trees, with their spreading root systems, have a competitive advantage in areas
underlain by cohesive, day-rich soils. Coniferous trees, on the other hand, contain primary tap roots and are best
suited for areas underlain by well-drained, sandy soils.
6. Analysis of Land Use. Land-use patterns can be additional indicators of underlying soil conditions. For
example, croplands are generally composed of relatively fine-grained soils, whereas transportation networks and
urban areas are normally sited on well-drained, relatively coarse materials. Such land-use factors should be taken
into account when analyzing aerial photographs.
7. Analysis of Pattern. The combination of tone, erosional effects, drainage, landforms, vegetation, and land use
make up the pattern of an aerial photograph. Similar soils that are derived from the same type of parent material,
deposited in similar fashions, and occupy similar topographic positions will, under the same environmental
conditions, usually exhibit similar photographic patterns. Dissimilar soils, on the other hand, are represented by
8. Analysis of Geography. The physical geography of an area is the result of its geologic history and the
prevailing climatic conditions, as manifested through the combination and arrangement of erosional
characteristics, drainage features, topographic landforms, vegetational occurrences, and land-use patterns.
Successful interpretation of the geography of a region often leads to the relatively accurate classification of soils.
PART D - RECORDING REMOTELY SENSED SOIL INFORMATION
Soil information derived from remote interpretation is recorded graphically as a soil factor overlay (see figure 3-
7). Table 3-2, page 3-20, contains tabular information regarding the properties of individual soil units depicted in
Preparing a soil factor overlay and its associated soil data table includes the following procedures: