Geoscience Reference
In-Depth Information
9.1.1 g
eograPhic
S
ySteMS
Geographers easily agree on whether a certain part of the world can, or cannot, be called a
geo-
graphic system
. It is hardly possible, however, to provide an operational definition of this notion,
and the problem arises from the second part of this term, that is,
system
. Expressed in a general way,
a system is 'a set of components together with the relations connecting them to form a whole unity'.*
Ludwig von Bertalanffy (1968) popularised the notion of a system, beyond the world of physics,
stressing the importance of
open
and
self-organising
systems that exchange matter and energy
with the outer world and change their internal organisation by themselves. When formulating his
approach, Bertalanffy had biological and ecological systems in mind, but the basic notion behind a
theory of systems also applies to geographic systems.
The goal of GC, in the broadest sense, is to understand quantitatively the structure and dynam-
ics of geographic systems. General systems theory helps us to establish an epistemological frame-
work for this purpose. According to Bertalanffy (1968), to specify a geographic system, we should
(1) define the objective of the study, (2) outline the components of the system and the interactions
between them and (3) define the laws governing the system's dynamics. For geographic systems,
the second requirement is concerned with specification of the spatial and temporal resolution of the
system and defining the rules for locating the components of the system in space, while the third
with the laws governing relocation of system components and locating emerging components of the
system. Often, we are interested in the dynamics of a geographic system that is dependent upon
external,
control
, parameters (Haken, 1983).
9.1.2 a
gent
-B
aSed
V
iew
of
a
g
eograPhic
S
ySteM
: a
n
i
inforMal
e
xaMPle
To move from a general to an operational view of AB systems and models, let us consider the
dynamics of horticulture in the African savannah, where the stable production of food is a major
problem. This example originates from the recent USAID project in the Kita administrative area
(25 × 25 km), Mali (Kidron et al., 2010; Grinblat et al., 2014). The goal of the project is to assess
if Mali's traditional agriculture will be able to supply, during the next decade, enough food for the
growing population of the country.
To describe the horticultural dynamics in Kita, four system components are necessary: (1) lands
that can be potentially used for agriculture, represented by
fields
; (2)
farmers
who decide on the use
of these fields; (3)
crops
; and (4) the
regulator
, who issues land-use permissions and is responsible
for the price of fertilisers. Two interactions are important for understanding the functioning of the
system - between the farmers and their fields and between the regulator and the farmers.
The laws governing the dynamics of this system are simple. Every year, the farmer decides to
extend or reduce the amount of cultivated area and selects the crops that will be cultivated in each
of the fields, taking market demand into account. The yield of the chosen crop is a function of the
properties of the soil, the use of fertilisers and the weather. The regulator forces the farmers to
cultivate or restricts the activities of farmers through the provision of land-use permissions and the
fixing of fertiliser prices. The dynamics of the system are defined by the decision-making rules of
the farmers, by the laws of soil dynamics, by the constraints imposed by the regulator and by two
multi-dimensional control parameters, that is, the climate conditions and the demand for the crops
in the marketplace.
To understand the dynamics of Kita's horticultural system, we must formally represent the
decision-making rules of the farmers and the regulator as well as the laws of soil dynamics. We
may then investigate the dynamics of crops, yields and soil fertility as dependent upon farmers'
and regulator's decisions and the control parameters. The model outcomes at the level of the entire
province are total and per farmer crop production, the fraction of the fertile fields and the fraction of
*
http://pespmc1.vub.ac.be/ASC/SYSTEM.html.
