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Simonson, 1989). The soil series is designated by the name of the place where the soil was Ýrst
identiÝed. When the series is established, it carries a description of the modal proÝle with infor-
mation on its distribution and relations to associated soils. The original idea considered that all
soils belonging to the same series constituted a taxonomic unit corresponding to a group of similar
soils (polypedons). For all practical purposes, series or phases of series have similar management
properties and respond similarly to management. As the basic map unit for detailed soil maps, the
series therefore represents both a
.
The evolution of the ideas concerning the concept of series eventually led to more precise tests
of deÝnition by selecting the most striking features enabling their differentiation: texture, drainage
class, organic matter content and distribution, color, and, eventually, ÑdiagnosticÒ horizons. The
inÝnite combinations have thus enabled the deÝnition of a very large number of soil series (currently
about 22,000 in the U.S.). The higher categoric levels in Soil Taxonomy are then built up by an
aggregation of the lower series, with adjustments made to the deÝnition of the higher levels to
accommodate the preconceived group of soil series.
Because of the conceptual difÝculties associated with this approach, a progressive dissociation
between taxonomy and cartography appeared, and the format of ÑtypologyÒ was developed. The
typology approach attempts to differentiate the concept of mapping, in the strictest sense, from
those of classiÝcation and taxonomy, which we believe are devices to structure our knowledge.
Subsequent to developing the two components independently of each other, their linkage could or
should occur (Baize, 1986; Jamagne, 1993; Buol et al., 1997).
Principles of classiÝcation, taxonomy, or reference may differ according to the school of thought.
The basis of several worldwide soil classiÝcation systems has been presented in a number of works
(Duchaufour, 1983; 1997). However, the majority of classiÝcation and taxonomic systems (CPCS,
1967; Soil Survey Staff, 1975; 1999), such as the Referential Systems (AFES-INRA, 1992; FAO-
ISRIC-ISSS, 1998) or map legends (FAO, 1988) concern the proÝles, sola, or pedons, and take
very little account of soil-landscape arrangements. The relationships between classiÝcation and
pedogenesis within the framework of ecosystems and soil-systems have nevertheless been revealed
on several occasions (Buol et al., 1997).
taxonomic unit
and a
map unit
CURRENT FRENCH IDEAS ON SPATIAL ANALYSIS IN PEDOLOGY
The “Pedological Cover” or “Soil Cover”
Soils, as we observe them today, are a result of transformations that affect the material of the
earthÔs crust. Successive climates and biological and human activities are the agents directly
responsible. Their effect depends not only on the nature of the rocks and their derived formations
that have resulted from them, but also the relief and the migration of matter in solution or in
suspension in water. The original arrangement of geological material disappears, leaving an entirely
new arrangement of pedological origin. We are obliged to recognize that soils are frequently, if not
always, a legacy of the past.
The processes of soil differentiation at the expense of a geological material are regrouped under
the designation of
. It is precisely this differentiation and the processes involved that
place soils in different soil systems.
pedogenesis
The factors of pedogenesis are well known: parent material,
climate, relief, water balance, land cover, time factor, and anthropic inÞuences.
The Pedological Cover, or Soil Cover, is a continuum that consists of all the soils distributed
throughout an area, an idea that tends to progressively overtake the more familiar concept of ÑsoilÒ
that appears today as a portion of this cover (Fridland, 1975; 1976). The distinction between soil
covers and the original rocks or materials is not always easy to carry out. However, some criteria
that enable soil to be distinguished from geological materials are the following:
