THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA 649
THE COORDINATIVE DEVELOPMENT OF BOOMTOWN
IN INDUSTRY, SOCIETY AND POPULATION
Qifan Wang Xinnong Yang
Shanghai Institute of Mechanical Engineering
Shanghai, China
ABSTRACT
The paper researches into a typical example of a developed
region with a boomtown of China, studies the coordinate
development of economy, and population migration of that region,
analyzes the mechanism and theory of industrialization and
urbanization of the rural area. A system dynamics model created
to study of urbanization is exhibited and explained. The paper
makes comments on current policy. And by the simulation, various
policies are examined, the paper finds out the more reasonable
coordinative growth rate and scale among industry, agriculture
and town construction. The interaction between a special region
and outside in’the process of industrialization and urbanization
is also a subject of discussion. The general conclusions and
suggestions on industrialization and urbanization of rural area
in China are put forward,
I. INTRODUCTION
The urbanization of rural population, in fact, is a dynamic
transition of the displacement from farming labor to nonfarming
labor or the migration of population from countryside to cities.
China is a country with a majority of rural population. Because
of the low productivity in agriculture and low speed of economy
development, the urbanization has stagnated for several decades.
A great number of surplus farming labors have been seeking the
outlet for improving their economic condition and income,
With the development of non-farming economy in developed rural
area, a large number of farming labors were moved into
non-farming labors. industry was developed rapidly. As a result,
the boamtown grew up in rural area.
1, The Difference Between City and Countryside
City and countryside are two different basic types of economic
and social living activities in function and structure, They
differ from each other, associate with each other, influence each
other as well, There are two main differences between them: one
is the gathering density of inhabibtants in living spaces, the
other is their different economic function in social life. There
doesn't and shouldn't exist a clearcut between them. Instead
there exist a lot of intersections, permeations, migrations and
interflows.
650 THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA
Each country has its own definition for urban population. During
recent thirty years, the definition in China has been improving.
It consists of two parts, one of which is the gathering level
the other occupation structure.
A city or a town is an area in accordance to one of the following
characteristics:
1) The place where the town or the government of a county(or
above that) locate.
2) The place where has habitants over 2,000, half of them are
non-farming population.
3) The place occupied by the big enterprises, railway stations,
business center, middle schools, scientific résearch institute,
and where has habitants below 2000 but over 1000, 75 percent of
nonfarming population,
Of the above, it is called a city that a area has over 20,000
habitants and where the government of county(or above that) and
big business locate. the rest are defined as town,
2. The Way of Urbanization
There are three principal ways of urbanization: The first way is
the direct migration from countryside into big or middle cities.
The second way is to build boomtown by government's investment to
attract a large number of surplus rural population, The third way
is the industrialization and urbanization of original countryside
by developing the local. rural economy.
The first two ways of urbanization are popular to most developed
and developing country. Considering China has the largest
population and backward economic level in the world, these two
ways are unsuitable for the urbanization of Chinese rural area.
For the spacious countryside in China, it must rely on itself to
promote rural economy, realize the transfer of the surplus
farming labors, take the particular way of the urbanization of
the rural population.
The so-called industrialization and urbanization of the rural
population means that proper percent of original farming labors
become non-farming labors and rural economic structure is
reformed, the urbanization of rural population can be realized.
This process is not isolated but related. The industrialization
of the rural economy can provide the conditions for the
urbanization of the rural population. The final purpose of
urbanization is to reform rural production structure, promote the
rural economy, make full use of the econemic resources and set up
the boomtown suitable scale for the development of rural economy
and the increase of living stardard.
THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA 651
II, DYNAMIC MECHANISM AND STRUCTURE
1. System's Overview
Urbanization is the inevitable result of economic development.
Nevertheless, the process 6f urbanization is a comprehensive
proccedure relating to the development of economy, society and
population.
Generally speaking, the development of urbanization depends on
political factor, productivity and economic structure, population
size, society and environment. Of all above, the economic factor
is the most essential one.
All four factors above are the basis on which we analyze the
urbanization system. We survey a particular system under the
relatively independent surrounding, make research into its inner
structure and mechanism, overlook the impact of surrounding.
Political factor is supposed as an exogeneous test variable. The
other three factors are considered as the main parts of system,
The development of urbanization is the result of the interactions
of economy, society and population in the system. If the model is
in specific surroundings(under the condition of policy and
external social economy), the behaviors of a system not only
depends on but also affects its inner mechanism and structure.
2. The Main Structure of System
The model consists of seven sectors as shown in Fig. 2-1. They
are agricultural production sector, industrial production sector,
population and migration sector, urban facility construction
sector, urban housing construction sector, land sector and
pollution sector. The figure gives relationships and influences
between each sector in the model, the kernel of which is
population and migration sector. From the Figure we can’see the
population sector connects with other sectors of the system, The
urban area is divided into four parts: industry, urban
facilities, urban housing and population. Countryside is divided
into agricultural production and rural population. In fact there
exist no clear edges between them, There are many rural labors in
the urban enterprises, also there are many urban enterprises in
the countryside. As the rural economic trading center, the small
town is closely related to the countryside. On the other hand, it
is also the reliable support of the agricultural production.
Though the urbanization of rural population is the inevitable
result of the rural economic development, it is not infinite for
the urban area expansion, as there are many limitations on the
development of urban area such as: allocation of land, labor and
capital shortage and etc.. However, it is the interaction of
these motivation factors and limitation conditions that dominate
the development of the urbanization.
652 THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA
[ POLLUTION z}
|AGRICULTUR] INDUSTRY
rs ns
I !
| feuray URBAN +] une
T~]porutarto POPULATIO —T FACILITIE
1 [
—— -
RABLE LAN RBAN LAND URBAN 7
HOUSING-
Fig. 2-1 THE OUTLINE OF THE MODEL
ECONOMIC LEVEL:
. > a
‘THE RATE OF 1D DEMAND + URBAN. ISTRUCTIGN—t~ AVAILABLE LAND
FARMING PRODUCTION, + + \ a ; —~_
A . + 3
SUPPLY-DEMAND RUB URBAN POPULATION NON-FARMING
Ra POPULATION + ECONOMY
+ +
ios Se LABORS sure
+ +
+
FOOD OUTPUT ‘ARABLE LAND — pay ha’
Fig. 2-2 THE CAUSAL LOOP OF MAIN VARAIBLES
THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA 653
3. Causal Loop and Feedback Mechanism
The causal loops of principal variables of the system are shown
as Fig.2-2. The urban population comes from non-farming labor.
And urban facilities and scale determine the migrating speed and
degree from non-farming labor to urban population. There are
three factors which affect the transfer from farming labor to
non-farming labor: The first one is rural surplus labor. The
increase of agricultural productivity and decrease of arable
makes many rural labors overflowing. That forces them to seek new
economic activities out of farming; The second one is the booming
of urban employment. The rapid development of non-farming economy
provides more jobs for rural surplus labors and attracts a large
number of farming labors from rural area to urban area; The third
one is the supply-demand rate of food. Only if food output meet
the demand, is it allowed for farming labor to transfer to
non-farming production.
Feedback loops of the model include three dominant positive
feedback loops and four dominant negative feedback loops.
III. THE CONSTRUCTION AND TEST OF SDMURP MODEL
Based on the quantitative analysis, system dynamics model of
urbanization of rural population(SDMURP) was constructed by means
of DYNAMO language. The model consists of about 400 equations,
including 11 level variables. The manipulation of the model is
operated on computer VAX-11.
The construction of a model is a proccedure of comprehension and
disintergration. It is also a proccedure of studying inner
structure and function of a system and solving problems.
The construction of a model has gone through many steps. The
principal ones of them are as follows:
1) The Improvement and Adjustment,
The primary model was separated into several sectors. Each one
was tested and improved separately to determine the basic
structure and parameters of the model, which is called partial
test.
Following the partial test, the model was integrated gradually,
tested in its entirety, revised and even reconstructed until the
model satisfies the demand,
2) The Verification of the Model
Determining the vertibility of the model, i.e. the research and
adjustment work on decisive degree of a model is known as the
test and verification of the model.
The model has experienced the test under extreme condition,
parameter estimate and sensitivity analysis, The outputs of the
654 THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA
model approximate to real history data with satisfying degree of
precision, The difference of main variables ranges from 1.4 to 9
percent, The testing results of the model prove that the model
give reasonable output under extreme conditions, the structure of
the model is stable and reliable.
IV. A SPECIFIC EXAMPLE OF REGIONAL ECONOMIC DEVELOPMENT AND
URBANIAZATION
1. The Conditions and Surroundings of the Base Run.
1) In the population and migration sector, it is supposed that
the natural birth rate is around 0.9% and migrating multiplier
variable named NMMRT equals 0.1, which determines the population
migrating rate with urban housing factor(AMMHT), urban public
servics fdctor(AMMPS) and population crowding factor(AMMCT).
In simple way, the fraction of labor forces to population is
around 502.
2) In housing construction sector, the normal constructing rate
variable named HCFB equals 0.017, which will be adjusted by urban
land factor and housing supply-demand factor.
The housing standard is 12 square meters per capita.
The housing lifetime is 100 years.
3) The normal constructing rate of urban construction is named
NPSCF which will also be adjusted by urban land factor and demand
factor.
The average lifetime of urban public facilities is 50 years.
4) In agriculture production sector, the output rate of the
agricultural capital named ALPHAA equals 0.2.
The multiplier of potential farming output named MPOF equals
0.326.
The normal increase rate of land output named NIR equals 0.06.
Food demand (FD) consists of three parts: one is the food
purchased by state; another is the food left; still another is
food ratio.
The allocation of farming capital investment named NFEFP is a
decisive variable which can act as either policy test variable or
intrisic variable. Normally it equals 0.84.
5) In industrial sector, the elastic coefficient of industrial
capital in Cobb-Douglass function is 0.5 named ALPHA, Normal
fraction of industrial investment named NFCIR is 0.13,
THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA 655
2. The Results and Comments of Base Run
Under the condition and surrounding stated above, the model gives
out the results of developing tendency of society and economy of
the region from 1975 to 2000.
1) Urban Facilities Trend
Yangshi district began its urban construction in 1983. The
development of. urban facilities is rather quick, but nowaday
state of population is that gathering population has been up to
10000 while residents are only about 3000 and that a large
quantity of people commute between urban area and countryside.
This is due to the present rural economic structure and urban
residential condition, In terms of recent urban constructing
speed and scale, the developing curves of urban occupying area,
housing construction and urban facilities are shown in Fig 4-2.
From the result of the model, we can see that all the urban
facilities are increasing constantly before 1990, but they are
limited after that time as the urban available land shrinks.
Another group of curves show the incomformity and
unreasonableness of the development of urban facilities. Fig 4-1
is the availablity curve of the urban facilities. The curve of
housing availibility per capita is declining from 1975 to 2000.
Although the curve of the capital of urban services availibility
is declining from 1975 to 1983(the standard value is set as fixed
capital of urban facilities at the starting year), it has the
tendency of growing in the ensuing year which will soon be
restricted by the limited urban land, And it is estimated that it
will be greatly declined in the last ten years ‘of this century.
And the living urban area will have the same changing trend.
2) Population Growth Trend
According to current policy of population migration and
developing scale and rate of urban construction stated above, the
developing tendency of urban living and gathering population is
shown as Fig 4-3, The simulating results show that in the future
urban area of that region, the gathéring populatin will make up
the overwhelming majority of population, but the living
population constitutes a small fraction. the urban population
grows slowly and the mechanical increase rate (migrating rate). of
population is declining rapidly.
3) Industrial Developing Trend
Fig. 4-4 is the curve of industriak developing tendency. From
1975 the industrial output value seized ‘the dominant position.
The industrial output was: booming from 1979 and the increasing
rate of its output value keeps risng until it reached its peak in
1980. In the following year, it declined but was kept over 20%,
the increasing rate of industrial output value will decline to 8%
in the next 15 years. According to the current policy of
industrial development, fixed capital of industry will be keeping
increasing from 1985 and industrial scale will be expanding.
Whereas, with the rise of occupying rate of urban land, urban
656 THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA
-AVAILABILITY OF PUBLIC SERVICES
APS--
HOUSING SUPPLY-DEMAND RATE
0.0r 5.0r i0.0r 15,0r
2 0.0 0.5 1.0 1.5
re tyros
4
3
2
a
z
=
a
&
&
& 1965.9
3
2
e
8
g
Es
2
2 139500
g
gq
a
a
B
vi 986t-490-4
LLPC---LIVING LAND PER CAPITA
HOUSES~--HOUSING AREA
POPT---POPULATION OF URBAN AREA
CUPS--~CAPITAL OF PUBLIC SERVICES
5.0004 19.0004 15.000 20.000 GIRS
x 19:00 ire '
SOUP Parsi pau “ator er
20:00 50.000 0.000 70.000
3 eH
®
s
'
& 38
3
FA
5
3 FL
a 196560 ee
3
5
g ©
= .
8
g a
g
Es
2
Ss s95.0
a
a
5
2
2
THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA 657
POPT---POPULATZON OF URBAN AREA
POPGT---GATHERING POPULATION OF URBAN AREA
0.0r 5.0r 10.0T 15,00 DO.
1975.09)
1Seu
1945.5
NOILVINdOd NVEYN. AO HIMOYD INL €-y “Bta 8
IRIO--~INCREASE RATE OF INDUSTRIAL OUTPUT
I0---INDUSTRIAL OUTPUT
1985.9}
XALSNGNT JO aNVA Anaino 9~y°8t4
1995.9]
658 THE 1987 INTERNATIONAL CONFERENCE OF THE. SYSTEM DYNAMICS. SOCITY. CHINA
available land will be reduced rapidly, which constraints the
expansion of industrial scale. From the curve in Fig. 4-5, we can
see that the increase of fixed capital will tend to be flat in
1995, capital accumulating rate also reduces constantly.
Thercfore, it can be learned that increasing output by the
expansion of industrial scale through investment on a large scale
will be restrained by limited land.
4) The allocation of labor force
Fig. 4-6 shows the curves of labor transfer, From the curve of
industrial labor, it can be seen that there are only 1500
industrial labors but farming labors are up to 8000 which make up
79% of total labors. With the development of rural industry, a
great number of rural surplus labor forces were displaced to
noh-farming businesses.There is a turning point in 1980 when
industrial labors began to surpass farming labors, which marked
the rural economic structure begining to transfer from dominant
by farming production to industrial production. Four fifth of
§ abors has been transfered to non~farming labors, whereas farming
‘Labor decreased to 1020 only making up 7.5% of total labors. Up
=to 1985, an industrial ecnomic system on certain scale had been
‘set up,.the displacement of labors had been finished. From 1985,
the.developing curve will keep stable and be ralatively balanced.
Industrial labors can't meet’ the demand all the time. Through
surveying the whole developing proccedure, the labors development
of -Yangshi district will-experience a process as follows:
SURPLUS ------- SATURATION ------- SHORTAGE
That will be a new approaching problem.
5) Agriculture Developing Tendency
After the.low tide of farming products in 1983, the farming
products had risen next tow years. However, the declining
tendency.‘of capital and labors input of agriculture dosen't stop
at that time. Delay effects of declining of capital input and
constant reduction of farming labors makes farming products
shrink rapidly. From the fig. 4-7, it can be seen that the
agricultural production will give rise to a crisis. Food supply
will be largely below food demand, which will cause unavoidable
serious effects on ecnomy and people's living standard of that
district.
3. The Research on Reasonable Developing Plan or Strategy
As stated above, there are many’ obstacles and potential crises in
urban, population and economic development. The analysis last
section show possible problems. in the future developing tendency
of that region, In this section, we will seek the reasonable plan
or strategy and select quasi-optimal developing policy to solve
the potential crises and problems.
1) The Suitable Range of Urban Land
As stated above, the development of urban facilities and industry
will be constrained by available land. Therefore, the first
THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA 659
ACCUMULATING RATE
CAPITAL IN INDUSTRY
0 0.04 7.0K IN.ONE
fa ie 82 88 O:8 * HeoeR
° ADT Gee
rs
;
&
FJ
5
on
fe
5
g
2 1985.0
&
a
2
2
S
=
é
2
2
B 499569
3
5
2
3
B
Es
LFI---LABOR FORCES IN INDUSTRY
FL---FARMING LABORS
4g) LBTP-—-LABOR FORCE IN SERVICE PRODUCTS
oor 5.0 10.07 15,07 0.0
A9E Dey >
Z i"
& :
:
i
& :
FE _
a .
Q 4
SG 1933.0) -3ee fo - 2 - - - ee - - Sees
2 5 : :
a H :
8 5 ;
ef at
8 3 f— Fe:
e 3 E
B is9s.afs~ et eee tees
a 3 .
3 3
a 3 a
i=} > I
5 : 5
660 THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA
=
ot
aa
ze
aN
gr
I
&
< =
= ao
a i
z
<
=
bid
pa
can)
BpHOe
DwZzD
BEEZ
ON
ODHD ae |
ZARORS I
=I
=aaa
ROOD
<S095
a Fi Fea Fe
rere
1 I
baad
Se ee oS 2 e
Roe re ry
z 3 a
Fig. 4-7 FARMING OUTPUT AND FOOD SUPPLY-DEMAND RATE
THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA 661
problem to be solved is to determine minimum arable land and land
occupied by urban facilities and industry. If we make a
pessimistic estimate on the output rate of land, it can be
supposed that only if arable area is kept over 112600 acre, food
supply can meet food demand, from which it can be reasoned that
the suitable urban area is around 3.5 square kilometers.
2) The Appropriate Scale of Urban Population
The growth of urban population depends on the level of facilities
and urban scale, but more important one is the policy of
population migration, According to nowaday migrating policy, the
migration of population is so slow that it can't meet the demand
of urban development and economic increase. Through tests and
selection by means of simulation of model, it is suggested that
the appropriate scale of urban population be around 10000.
The growth of urban population of that region is mainly due to
mechanical increase of population, i.e. migtation. As shown in
Fig. 4-8, the mechanical .sncrease rate of urban population will
be up to 10% per year and 600 persons per year, reach the peak in
1995,
3) The Strategy of Development of Urban Facilities
The rapid growth of urban population and development of urban
economy raises the new demand to the construction of urban
facilities. From the simulation of the model, the level of urban
housing per capita and urban facilities will be much lower than_
the standard,
On the problems above, the following strategy is suggested:
First, the housing contructing rate, should be increased greatly
The housing construction rate should be increased by 50%.
Second, urban land should be distributed with reasonable share
among urban services, industry and housing construction. The
policy of urban land distribution shown as Fig. 4-9 is. suggested.
Three curves in Figure. suppose that when available land is
sufficient, there will be no limitation to all three sectors.
With the decrease of available land, more limitation will be put
on industry, but the preferential treatment will be given to
urban housing and facilities construction.
In accordance with the. policy stated above, the simulating output
is shown as Fig, 4-10, which states that the availability of
urban housing and services satisfy the requests. All facilities
develop with reasonable fraction. The housing availability is
over 1 and living space per capita is over 42 square meters,
4) Simulating Test of Industry
By analysis, land and labors are the principal affecting factors
to future development of industry. Of limited labors and land
resourses, it is the most important and key problem how to
distribute and make full use of those resources to coordinate
with the development of urban facilities and indusrtry. It is
suggested that technology progress should be speeded up. The
662 THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY.. CHINA
PIMRR---PURE IN-MIGRATION RATE FROM RURAL AREA
POPULATION OF TOWN
PBRT---PURE BIRTH RATE OF TOWN
BR-—-GIRTH RATE
o.coor ; x SOE BE Pnee, eer
198560
199.9)
WidOd NVE¥ JO ALVY ASVAYONI BHL g-y -Byy
PAGE= 1
EFFECT OF LAND ON SERVICES CONSTRUCTION
EFFECT OF LAND ON INDUSTRIAL CONSTRUCTION
-~-EFFECT OF LAND SHORTAGE ON HOUSING CONSTRUCTION
i
cs
NOLLNGTYLSTO GNVT JO HANNO AOTIOd BHL 6-7
THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA 663
investment of funds and the increase of educational level will
promote the development of technology. From 1986 to 1990, the
accumulating rate will be reduced to around 30%, and the capital
investment of industry decreases within that periods. The capital
will be used to develop urban construction, After 1991, with the
increase of marginal output rate. of capital, the capital
investment should be increased which will make industry develop
constantly. Fig 4-11 shows the developing tendency of industry
after improvemnet. :
5) The Reform of Agricultural Production
the analysis of agricultural production in the last section -
suggests that main reasons for the reduction of farming output
are the reduction of capital investment and labors. On those
problems, it is suggested that farming labors. be kept over 1500,
and that farming capital investment should reach 600 yuan per
acre as early as possible.
Vv. CONCLUSION
With the high speed development of rural business economy in
Yangshi district, the surplus labors in the district has been
displaced. But that doesn't mean the urbanization has met the
requests, The period from 1985 is just the-begining of
urbanization of population. Migratory Iabors.is only the result
of the uncomplete development of urban facilities. Therefore, to
make population urbanized it needs not only “the development *of
non-farming economy but also the development and construction of
urban facilities, From the simulating results showed above, we
can conclude that:
In future 20 years, the investment on industry development should
be reduced, on the contrary, the investment on urban construction —
should be increased. More attention should be paid to the
construction of urban facilities especially urban housing. The
urban area scale is supposed around 3 square kilometers and the
suitable urban population will be 10000 by the year 2000.
The current policy of population migration will not be of benefit
for reasonable distribution between urban and rural area. More
migrating from countryside to city should be encouraged before
2000. :
To keep the food output meet the food demand, the arable land
should be kept over 112600 acres, farming labors over 1500 and
farming capital investment reached 600 yuan per acre as early as
possible,
The future development of industry mostly relied. on the
technological progress. Therefore it is more imperative to
promote the technic level and educational level of industrial
labors.
664 THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA
APS---AVAILABILITY OF PUBLIC SERVICES
HSDR---HOUSING SUPPLY-DEMAND RATE.
POPT---POPULATION OF URBAN AREA
LLPC~--LIVING LAND PER CAPITA
7 8 OF DA
er ag Be ae 28 Ries
Sy 0 90.0 6,0 70. .
E1975 .0
>
a
3
a3
=
BE
5
BE. wses.a
ce ;
Be bh
Ag .
g
=
Z vavss.e ‘
E
5
|
g
B
LFI~--LABOR FORCES IN INDUSTRY
‘TEI---TECHNOLOGY IN INDUSTRY
I0---INDUSTRIAL OUTPUT
CI---CAPITAL IN INDUSTRY
OL r 5
88 3g Ro Bo"
eer v é
1985.4
1995.04
XMESHONT. JO AONTINGL
ONIAOTAARG ATAVNOSVAY SHL-Ti-> "3ta
THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA 665
SDMURP model is.constructed on the purpose of planning the
coordinate development of regional urban facilities and economy
with population growth and migration. Through a Example showed
above, it is proved that the model describes the actual
Structures and dynamic behaviours of the real system, give out
reasonable results. Therefore it can be concluded that the model
is successful and useful although there are some structures and
machnisms needed improving, and it provides an effective and
scientific tool for solving urban and regional problems.
REFERENCES
Forrestor, J.W.,1961, Industrial Dynamics, Cambridge, Mass, The
MIT Press
Forrestor, J.W.,1969, Urban Dynamics, Cambridge, Mass, The NIT
Press
Forrestor, J.W.,1977, World Dynamics, MIT Press
Gordon, Geoffrey, 1979, System Simulation, Prentice-llall, Inc.,
New York
Helly, Walter, 1975, Urban Systems Model, ACADAMIC PRESS, London
CC BY-NC-SA 4.0