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SPATIAL INTERACTIONS
Dr. Julius Kivelia Department of Geography University of Dar es Salaam
Outline 1. 2.
Introduction Concept of Spatial Interaction
Bases/conditions for spatial interactions to occur Models of Spatial Interaction
3. 4. a. b.
Ullman’s model The Gravity Model
The Role of Transport & Communication
5.
1. Introduction Geog = a discipline of spatial variations, focusing on how humans organise/use space variably. It deals with how:
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1.
Humans interact with earth’s surface to produce material goods
2.
Earth resources & people’s efforts (technology) vary spatially, resulting to spatial differences in types & patterns of settlements, production opportunities, etc. 1
+ 2 result to spatial variations in goods produced hence creating conditions of demand & supply, causing SPATIAL INTERACTIONS
2
Concept of Spatial Interactions
Movements between places
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people, commodities, ideas & technology Observed through flows ➢Migration/commuting ➢
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Trade ➢Technology Facilitated by transport & communication ➢
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3. Conditions for spatial interaction ◼
For spatial interaction to occur there must be: Uneven distribution of:
1. 1. 2.
resources and technology,
The uneven distribution creates points of supply and demand between locales, thus necessitating flows of people, commodities, ideas, etc.
Conditions cont’d People’s awareness of:
2. a. b. c.
Locales of demand & supply Transport – modes/types & costs Ability to pay
Principles to govern interactions
3. a.
Tariffs, policies, controls, etc.
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Uneven distribution, people’s awareness & principles governing interactions result to different types & patterns of flows ➢ People, commodities, technology, ideas
4. Models of Spatial Interactions Try to explain interactions between places, focusing on:
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Why interactions occur 2. Patterns/magnitude of interactions 1.
Different spatial models like:
◼ 1.
Ullman’s Spatial Model
2.
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The Gravity Model
The models also consider the role of transport & communication
4.1 Ullman’s Spatial Model Seeks to explain why interactions occur/ do not occur between places Explains interactions as governed by three factors, namely:
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1. 2. 3.
Regional Complementarity Inertvenning opportunities Spatial transferrability
Regional Complementarity ◼
Existence of conditions of supply of specified goods in one region and its demand on another region
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A function of differences in resources available in the respective regions, which in turn causes a situations of demand and supply
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Example: ➢
Region A produces goods X. Region B does not produce it
➢
Region B has demand for goods X. In addition, Region B has factors which make the demand to be effective:
Is aware of the supply of goods X in A ➢ Has desire for goods X ➢ Has the purchasing power for goods X ➢ Knows of means of transport between A & B ➢
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The TWO sets of conditions in the two regions, i.e. supply in region A and demand in region B, plus the other four conditions (awareness, desire, purchasing power & transport) in B creates an environment of effective
supply and demand between the two regions, hence complementarity between regions A and B
Intervening Opportunities ◼
Is the existence of other regions that can serve as alternative sources of supply & demand for the intended goods, thus intervening the supply & demand conditions in regions of complementarity ➢
Interactions will occur if there are no intervening opportunities in the sets of conditions for complenentarity,
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e.g. if there are no alternative supplies, better prices, transport, tastes, etc.
Where intervening opportunities exist, interactions will not occur between the regions with conditions of effective supply & demand. People will seek alternative regions with: ➢
Better prices, better tastes, etc.
Transferability ◼
Existence of conditions that allow (make possible) the movement of commodities, people, technology, ideas, etc. ➢ A function of: distance (measured in real costs & time) ➢ Specific characteristics of the product (bulkiness, weight, persihability, etc.) ➢
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Without the factor of transferability, interactions will not occur as people will
seek alternative products in regions where transferability is possible.
FOOD FOR THOUGHT 1.
Outline the factors of interaction in Ullman’s Spatial Model and comment on the relevance of the model in explaining rural-urban interaction in a country like Tanzania
To what extent are the conditions of interactions relevant to situations like Tanzania?
2.
The Gravity Model ◼
An econometric model which seeks to explain patterns and magnitude of interactions between places ▪
Proposed by Tinbergen (1962); various improvements since then
▪
Anderson & Van Wincoop (2003) Helpman, Melitz & Rubinstein (2005)
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Called gravity model b’se it originated from Newton’s Law of Universal Gravitation
Newton’s law of Universal Gravitation ◼
Masses attract each other The attractive force (interaction) between two objects is proportional to their masses and inversely proportional to their respective distance
o
o
Larger masses have a larger attractive force than smaller ones Masses close together have a greater attraction force
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Newton’s Law determines attractive force by multiplying the masses of the two objects and dividing the product by the square of the distance Expressed thus:
Fij = MiMj Dij2 Where: F = attractive force; M = mass; D = distance.
Gravity Model of Spatial interactions Analogy of Newton’s law
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Predicts magnitude and patterns of flow of people, goods, information, technology, etc. between two populations based on Newton’s Law of Gravitational forces
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Larger places attract flows more than smaller places Places closer together have a greater attraction GM determines relative magnitude of interaction between two places by multiplying the population of place 1 with that of place 2, and dividing the product by the squared distance between the two places
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Expressed
Fij =
thus:
PiPj Dij2
Where:
F
ij = flows from i to j
(or total flows, i.e. Fij + Fji ) P = population size D = Distance between the two locations ◼
GM explains spatial interactions better when presented as an econometric model Xij = K YiąMjβ
Tijθ Where:
X
ij = exports from i to j
(or Total Trade, i.e. Xij + Xji ) Y = economic size (GDP; POP) T = trade costs ◼
GM explains interactions on the basis of:
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Distance between places; ◼ The population size ◼ Size of the economy, etc.
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Can explain the magnitude and patterns of flows of migrations, goods, ideas, etc.
Opponents views ◼
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No scientific evidence, only observations; Biased towards historic and social ties and towards largest centres ◼ Perpetuating status quo.
5. Transport & Spatial interactions ◼
Transport = important in: 1.
Demand & supply side of complementarity Materials, manufactured goods, people, etc.
➢
2.
3.
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Transport has to be efficient in terms of: ➢
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Opening up remote/new areas for habitation, exploitation of NRs (agric. hearths, mining deposits, trade centres, etc), thus creating conditions for interactions Facilitating interactions, which in turn depend on costs influenced by mode of transport, distance, characteristcs of products, etc.
Integrating geographical zones (properly networked to facilitate spatial coverage) Costs – finance & time (depend on MoT)
Yet, an efficient transport network is expensive
➢ ➢
Initial capital, running costs, maintenance, etc.
To what extent does the African transport network facilitate spatial interactions?
Overview of potentials & problems of transport in SSA ◼
Two complementary networks 1.
Indigenous – Paths, creeks, lagoons, rivers, lakes, etc. Highly integrated; non-mechanical
2.
Modern – railways, roads, waterways, airways
Skeletal (not well integrated), dendritic structure (feeding ports) Higher capacity; more efficient (cf indigenous)
Railways ◼
Railways – started 1895 – 1914 to facilitate colonial interests
➢
Demonstrate occupancy/title to territory Stimulate cash crop production Facilitate mineral exploitation
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Resulted into a patchy pattern
➢ ➢
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Some regions/countries with no railways ➢ Others with single arterial lines to the main port
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A few with skeletal networks, e.g. Tz, Kenya, Ug, Nig.
Roads Started with improvement of paths so as to provide access to waterways & railways ◼ Independent road networks were built from 1930’s to cater for inadequacies in transport network ◼
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Simple designs with low traffic density, then upgrades to today’s bitumen surfaces of high capacity
Today’s road networks: Are more integrated, (cf. railways); but not fully. Some areas are not networked Have a wider (not complete) spatial coverage Are of variable quality
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Seasonal roads All weather gravel roads High capacity motorways (bitumen)
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Have following limitations
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Some areas not served (remote, isolated from modernisation, etc.) Disparity btn road densities and pop. densities, topography, proximity to urban centres & areas with commercial agriculture Dendritic patterns which link hinterlands with ports Many are in bad conditions, not passable To what extent do they facilitate interactions?
Other Modes of Transport ◼
Rivers
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Short sections of low gradient, rapids/falls; Short navigable distances; broken distances
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Passing through areas of low transport demand, e.g. in the Congo Rain Forest
Mostly used in Congo & DRC, but with little efficiency because of numerous trans-shipments leading to increasing transport costs & time ◼
Airways
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Fastest but costly, not affordable to many Links African nations; also Africa with the rest of the world Not very important with regard to ruralurban interactions
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Pipelines
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Locally important for the transportation of commodities like mineral fuels & gas Links ports and landlocked countries (TAZAMA)
FOOD FOR THOUGHT 1.
2.
What do you think are the potentials and problems of transport development in Africa? What do you think are the strengths and weaknesses of transport systems in influencing spatial interactions in Africa?