Constantine P. Yialouris
Informatics Laboratory, Agricultural
University of Athens, 75 Iera Odos, 118 55 Athens Greece
yialouris@auadec.aua.ariadne-t.gr
http://www.aua.gr
Vassiliki Kollias
Soils Laboratory, Agricultural
University of Athens, 75 Iera Odos, 118 55 Athens Greece
lsos2kob@auadec.aua.ariadne-t.gr
Nikos A. Lorentzos
Informatics Laboratory, Agricultural
University of Athens, 75 Iera Odos, 118 55 Athens Greece
lorentzos@auadec.aua.ariadne-t.gr
Dionisios Kalivas
Soils Laboratory, Agricultural
University of Athens, 75 Iera Odos, 118 55 Athens Greece
lsos2kob@auadec.aua.ariadne-t.gr
Alexander B. Sideridis
Informatics Laboratory, Agricultural
University of Athens, 75 Iera Odos, 118 55 Athens Greece
as@auadec.aua.ariadne-t.gr
KEYWORDS: Expert system, geographical information system, land evaluation.
Acknowledgement The
present work has been produced as part of the project 'Development of
a Geographic Information System for Natural Resources Evaluation and Environmental
Assessment' (No. 91ED449), funded by the Greek Secretariat of Research
and Development. The authors are grateful to Professor Yassoglou
for providing the soil data of the area.
Since the mid 1970's, Expert Systems (ES) have been used in a variety
of application areas. One such area is the evaluation of natural resources
(Loh et al. 1994; Kettal 1994). ES applications
have successfully captured and focused human expertise in the evaluation
of natural resources. Some systems have achieved a level of performance
that compares that of human experts. The land evaluation procedures are
stored in a knowledge base and are used by an ES. At the same time, a Geographic
Information System (GIS) is used, to process and display spatial data (Pereira
et al. 1982; Rossiter 1990; De la Rosa et al. 1992; Bouma
et al. 1993).
The present paper concerns
the design considerations and the development of an Expert Geographical
Information System, EXGIS, which combines the capabilities of a commercial
GIS, PC ARC/INFO ver. 3.4, with those of a rule-based ES. This ES has been
based on a specially developed shell which satisfies certain requirements,
dictated by the Greek agricultural extension services. It has been implemented
in CLIPPER because the files produced by the latter (DBASE III+ files)
can subsequently be processed by ARC/INFO. EXGIS is currently running under
MS DOS. It is used as a tool for the assessment of land suitability for
certain agricultural uses. The motivations for the project were the following:
Figure 1 The study
area: the Pinios River basin of west Peloponesse in the south-western
Greece
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1. Maize |
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2. Olive Trees |
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3. Forage Crops |
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4. Citrus |
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5. Tomatoes |
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6. Fallow |
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7. Wheat |
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8. Vineyards |
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9. Natural Vegetation |
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10. Towns |
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Knowledge acquisition plays a crucial role for the development of a
reliable ES and requires the close collaboration of the knowledge engineer
with the domain experts. For the development of our system we followed
a knowledge acquisition procedure consisting of the following four stages:
Domain Acquaintance: This stage aimed at the acquaintance
of the knowledge engineer with the application domain. To this end, he
studied books and papers related to soil and land evaluation issues under
the guidance of the domain experts.
Meetings with the Experts: This stage aimed at the development
of an understanding of the experts' way of thinking. At the same time,
effort was made to elicit the experts' opinion for the ES's contribution
to soil evaluation procedure. To this end, two meetings were organised
with three soil scientists. After the second meeting, the experts were
asked to propose:
Soil requirements of : | MAIZE | |||||
FAO framework | S1 | S1 |
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Restriction levels of SYS |
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Parametric evaluation of restrictions |
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Soil requirements | ||||||
Slope | A | B | C, D | E | F | |
Drainage | A, B, C | D | E | F | G, H | |
Texture | ||||||
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3, 4, 5 | 2, 5 | 2* | 1, 2* | ||
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2, 3 | 2, 3, 4 | 2, 2* | 1 | ||
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2, 3 | 2, 3, 4 | 1, 2*,3* | 1 | ||
Soil Depth | >90 | (75, 90] | (50, 75] | (20, 50] | <=20 | |
Erosion | E0,E1 | E2 | E3 | E4 | ||
CaCO3 | 0,1 | 2 | 3 | |||
pH | (6, 7.5] | (5.5, 6]
(7.5, 8.3] |
(5, 5.5]
(8.3, 6] |
(8.3, 8.6]
(4.5, 5] |
(8.6, 8.9] | |
Organic Matter | >1.5 | (1, 1.5] | (1, 0.7] | <0.7 | ||
CEC (meq/100gr) | >18 | (10, 18] | (5, 10] | (2,5] | ||
Base Saturation | >70 | (50, 70] | (35, 50] | <=35 |
Climatic requirements of: | MAIZE | |||||
FAO framework | S1 | S1 |
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Restriction levels of SYS |
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Parametric evaluation of restrictions |
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Climatic requirements | ||||||
Average temperature during growth period | (22, 25] | (18, 22]
(25, 30] |
(16, 18]
(30, 35] |
(14, 16]
(35, 40] |
>40
<=14 |
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Average minimum temperature during growth period | (16, 18] | (12, 16]
(18, 24] |
(9, 12]
(24, 28] |
(7, 9]
(28 , 30] |
<=7
>30 |
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Average relative humidity during growth period (%) | (50, 80] | (42, 50]
> 80 |
(36, 42] | (30, 36] | <=30 | |
Average relative humidity during mature period (%) | (30 , 50] | (24, 30]
(50, 75] |
(24, 20]
(75, 90] |
<20
>90 |
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Sunshine during growth period (r/p)* | (0.5, 0.6] | (0.4, 0.5]
(0.6,0.75] |
(0.35, 0.4]
>0.75 |
(0.3, 0.35] | <= 0.3 | |
Sunshine during growth period (r/p)* | > 0.7 | (0.7, 0.5] | <0.6 |
General Knowledge Based Systems and GIS have been successfully used to develop Land Information Systems (He et al. 1992; Abdelmoty et al. 1994). EXGIS was developed as a tool which makes use of all the available information, to assist in the optimal allocation of land uses. It is an integrated Expert Geographical Information System and consists of two components, ARC/INFO and the ES Shell. Its architecture is shown in Figure 2. It was developed on a PC 486 IBM compatible microcomputer operating under MS DOS. We chose to build it in a PC environment in order to keep its cost as low as possible. ARC/INFO is used for the storage and processing of spatial data. The ES shell was developed for the purposes of the project. It has been implemented in CLIPPER because the files produced by it (dBase III+ files) can subsequently be processed by ARC/INFO. Interfaces have been written in SML (Simple Macro Language), the language provided by ARC/INFO, which integrate the ES and ARC/INFO under the same operating environment. A spatial database, a conventional database and a knowledge base are used to store and process the spatial data, the tabular data and the rules, for land evaluation.
<object>: drainage
<property>: IS. Other properties are <, >, =, IS NOT, etc.
<value>: B.
The conclusion of a rule represents the evaluation of a map unit for
a certain land use, with respect to a particular parameter.
The soil and climatic requirements
of each crop under consideration are used for the formulation of the ES
rules. For example, in the case of maize for the study area, Tables
2 and 3 contain
the soil and climatic requirements. A different knowledge base is built
for each crop. The modular design of the system enables its extension with
additional knowledge bases, one for each new crop.
As is obvious, the system development requires two tasks:
Build up the KB For a certain geographical area,
the experts and the knowledge engineer have to represent the domain knowledge
(soil and climate requirements of the crop) for each particular crop they
want to include in the KB.
Data acquisition and area digitization This task includes
a soil analysis for individual parts or the total area, meteorological
data collection of the area and digitization in the ARC/INFO. With this
procedure the necessary spatial and conventional DB are built having as
result the availability of a detailed map of the study area. The whole
area is divided into soil map units. Each unit has a set of properties
(characteristics) concerning the soil and meteorological information and
it has at least one characteristic with a different value from each neighbor
soil unit.
The system makes use of
the rules of the KB and the data of the spatial and conventional databases.
It can perform, according to the user's demand, the following:
For the region under consideration, a composite map was produced from
the overlay of seven available soil and land use maps, consisting of about
2,500 distinct map units. The farming units of the area are very small,
if it is taken into consideration that 3,500 ha with 10 different land
uses and 328 soil polygons resulted in 2500 distinct polygons with individual
soil - land use combinations. For each type of land unit, additional information
was also stored, concerning the use of fertilizers, agricultural management
practices and crop yield.
The seven soil maps were
transformed into the scale 1:20,000 and, using manual digitisation, were
stored in a spatial database created under ARC/INFO. The rectification
of soil maps was achieved with the use of topographic maps (1:5,000 and
1:50,000) of the Geographic Service of the Greek Army. The basic topographic
elements (e.g., roads, towns, main railways, rivers, contours and
coast line) were also digitized and stored in spatial files.
In the following paragraphs,
we describe the soil, climatic and land use characteristics of the study
area, as well as the basic methodology for land exaluation.
Figure 3 Lan suitability
for maize
The application of EXGIS to the area of Pinios has shown that, in their majority, the land units qualify for annual irrigated cultivation, with minor differences in maize, wheat and tomato. The excessive use of acidifying fertilizers (NH4)2SO4 has caused problems to some Alfisols of the area, the majority of which are slightly acid. In the last 30 years the pH of the affected soils has decreased by 1 to 1.5 units. Consequently, their suitability was downgraded by 1 or 2 classes. It has been estimated that approximately 15% of the Alfisol soils in which wheat and vineyards are cultivated are unsuitable for such crops, due to low pH values.
S1 | S1 |
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Maize | 2.55% | 61.00% | 36.45% | 0.00% | 0.00% | |
Tomatoes | 0.00% | 5.16% | 72.48% | 22.36% | 0.00% | |
Olive trees | 8.53% | 43.90% | 32.15% | 15.42% | 0.00% | |
Wheat | 0.56% | 7.58% | 91.86% | 0.00% | 0.00% | |
Vine yards | 2.06% | 60.16% | 26.44% | 11.34% | 0.00% |
EXGIS is a low cost but powerful prototype system for land evaluation.
Its modular design enables its easy application to various soil conditions,
climatic conditions and working environments. Since the requirements of
each crop are stored in a different KB the application of EXGIS to new
crops is straightforward, and no software amendments are required. The
evaluation of the system has been very satisfactory, i.e., the conclusions
drawn by it, match those of a human expert. Thus, the latter can be relieved
from a substantial amount of work.
Further work includes the
application of EXGIS to the evaluation of other Greek regions. In addition,
however, EXGIS is an efficient tool which can also be applied to other
areas, such as the management of the forestry ecosystem and land registry.
Optimal land use involves interrelated agricultural and economic decisions.
Thus the integration of the system with procedures for economic and environmental
impact analysis will produce a useful tool for land use planning.
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