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Land Management & Natural
Hazards Unit |
SOIL |
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Soil
Atlas of |
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A Soil Database of Europe
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Soil Geographical
Databases of Europe Introduction
The soil maps of Europe
contained in this Atlas are based on a collection of knowledge contained in a
databank known as the Soil Geographical Database of Eurasia. The database
contains a range of information on soil which is stored in several databases,
referred to as the:
These linked databases
represent a first step in the development of a fully integrated European Soil
Information System (EUSIS), the concept of which is described on Page 105 of
the Atlas. The information used to
create the maps of Europe depicted in this Atlas resides in the Soil
Geographical Database of Eurasia. This database is the result of a
collaborative project involving all the European Union Member States and
neighbouring countries through participation in the European Soil Bureau
Network (see Page 104). How does the database work?
The Soil Geographical
Database of Eurasia is a simplified representation of the diversity and
geographical variability of the soil coverage at a European level. It is
based on Geographical Information System concepts (see Page 97). The database is composed of a
digitised soil map (digital or computerised representation) that is made up
of closed contours called polygons. The soil map is at a scale of 1:1,000,000
where 1 centimetre on the map represents 1 kilometre on the ground. At this
scale, it is not possible to draw very small polygons, so it is not possible
to draw directly the delineation of individual soil types. Thus, the soil map
represents the delineation of groups of soil types that are called Soil
Mapping Units or SMU for short. Soil Mapping Units correspond to the polygons
that are defined by the same group of soil types. The groups of soil types
are generally defined as areas in the landscape where the same soils are
present, in the same position and which have functioning relations between
them. Each SMU contains one or more
Soil Typological Units (STU) which are individual soil units that can be
described by parameters (or attributes) specifying the nature and properties
of the particular soil (for example the texture, the water regime, the
stoniness, WRB code, etc.). This information is stored as a separate table called
STU Attributes. To describe the properties of
the soil types, several tables are available forming the semantic dataset.
The first table, called SMU, contains variables (named also as attributes)
that give information about the SMU. The second table, called STU, contains
the information describing the soil types, named in the database Soil
Typological Units (STU). These variables give information about the nature
and the properties of the soil like its texture, its name in WRB
classification, its parent material and so on. A third table, called
STU.ORG, gives the list of the STUs that belong to each SMU with the
percentage of area they represent within the SMU. When the SMU is composed of
only one STU, this percentage is equal to 100. When the SMU is composed of
several STUs, then the sum of the percentages is equal to 100% (for example
in the figure on this page, the SMU 1 is composed of the STU 11 representing
70% and of the STU 10 representing the remaining 30%). The data are stored in a
relational database management system that enables to define relations
between the polygons, the SMU table, the STU.ORG table and the STU table and
which are symbolised on the figure by arrows. These relations enable the
transfer of information from one object to another and are very useful to
make maps from the Soil Geographical Database. How do you deal with more than one STU?
By now, you will have
realised that, in many cases, there will be several SMUs with more
than one STU. But, soil properties are described for the STUs, not for the
SMUs and generally, the STUs that belong to the same SMU have different
properties. |
So, how is it possible to draw a map for a soil property? This is possible using the relations between tables and polygons. The most common way to make a map of a soil property is to determine a dominant STU within each SMU. This can be done using the STU.ORG table where the percentage of area of each STU within a SMU is given. Then, the dominant STU within a SMU is the STU having the higher percentage of area. Then, you just have to take the value of the dominant STU for the soil property you want to map and to assign this value to all the polygons that form the SMU. It is important to keep the indication of the percentage of area corresponding to the value drawn on a map. In the above method, it is the percentage of area of the dominant STU. This percentage can also be drawn on a map. Such maps are called purity maps and give important information about the variability of the soil property within the SMUs (see the figure of the bottom of the page). The higher the percentage, the lower is the variability inside the SMU. Producing the maps for the AtlasTo produce the maps shown in the Atlas, a procedure was carried out to take the dominant value per SMU using an automatic procedure developed in the GIS. Be careful in using these maps?The Soil Geographical Database of Eurasia results from a synthesis work done by national soil scientists in each country by expert judgment. Thus, the accuracy of this work is depending on the state of knowledge of soils and the availability of more detailed soil information in each country. Thus, quality indices of the information are important to look at, like the purity maps or confidence level for estimated data (see Page 99).
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