Some Questions What would induce emigrants to leave everything behind and risk everything on moving elsewhere? What considerations influence how individual.
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Some Questions What would induce emigrants to leave everything
behind and risk everything on moving elsewhere? What considerations
influence how individual human beings use space and act within it?
Are there discernible controls on human spatial behavior? How does
Distance affect human interaction? How do our perceptions of places
influence our spatial activities? How do we overcome the
consequences of distance in the exchange of commodities and
information? How are movement and migration decisions reached?
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Spatial Interaction: the movement of peoples, ideas, and
commodities (goods that are bought and sold) within and between
areas. Some familiar examples: International trade, semitrailers on
the expressway, radio broadcasts, and telephone calls. Movement of
whatever nature represents the attempt to smooth out the spatially
differing availability of required resources, commodities,
information, or opportunities.
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Bases of Interaction Neither the worlds resources nor the
products of peoples efforts are uniformly distributed. Commodity
flows are responses to these differences. Matters of awareness of
supplies or markets, the presence or absence of transportation
connections, costs of movement, ability to pay for things all and
more are factors in the structure of trade. Edward Ullman
(1912-1976): observed that spatial interaction is effectively
controlled by three flow- determining factors:
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The three factors: Complementarity Transferability Intervening
Opportunities
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Complementarity For two places to interact, one place must have
what the other place wants and can secure. Restated: one place must
have a supply of an item for which there is demand in the other,
purchasing power with which to acquire it, and the means to
transport it. The word describing this circumstance is
complementarity. Just having different stuff though not enough to
initiate exchange.
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Brazil and Greenland have completely different resources, but
have almost no interaction because of lack of desire for goods. The
movement of crude and refined petroleum between spatially separated
areas clearly demonstrates complementarity. More generalized
patterns of complementarity underlie the exchanges of raw materials
and agricultural goods for money and industrial commodities.
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Transferability Even when complementarity exists, spatial
interaction occurs only when conditions of transferability are met.
Transferability: acceptable costs of an exchange. Spatial movement
responds not just to availability and demand, but to considerations
of time and cost. Transferability is an expression of the mobility
of a commodity and is a function of three interrelated conditions:
1. the characteristics and value of a product 2. the distance,
measured in time and money, over which it must be moved 3. the
ability of the commodity to bear the costs of movement
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If the time and money costs of traversing a distance are too
great, the exchange does not occur. Mobility is not just a physical
matter, but an economic one as well. If the cost is too great on
arrival to a buyer, trade does not occur. The buyer would either go
without, or find a substitute.
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Transferability is not a constant. It differs between places,
over time, and in relation to what is being transferred, and the
manner in which the movement occurs. The opening of a logging road
will connect a sawmill with previously inaccessible timber.
Increasing scarcity of ore will enhance the transferability of
lower-quality mine outputs. Transferability expresses the changing
relationships between the costs of transportation and the value of
the product being shipped.
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Intervening Opportunity Complementarity can be effective only
in the absence of more attractive alternative sources of supply or
demand closer at hand or cheaper. New York wont buy sand from the
Sahara desert region because it has a closer, cheaper supply more
locally. For reasons of cost and convenience, a purchaser is
unlikely to buy identical commodities at a distance when a suitable
nearby supply is available.
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Measuring Interaction The study of unique exchanges/events, is
suggestive, but not particularly informative. We seek general
principles that govern the frequency and intensity of interaction
both to validate the three preconditions of spatial exchange, and
establish the probability that any given potential interaction will
actually occur. We are looking for aggregate, not individual,
behavior.
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Distance Decay The lives and activities of people everywhere
are influenced by the friction of distance. Because there are
increasing penalties in time and cost associated with longer
distance, the exchange is more expensive, and therefore less likely
to occur. You visit nearby friends more often than distant
relatives. Students in college order out food when they are near
the restaurant, but dont if they live further away.
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Most interactions occur over short distances. Interchange
decreases as distance increases, a reflection of the increase in
transferability costs. Distance Decay: describes the decline of an
activity or function with increasing distance form the point of
origin. It is also evident however, that the amount or rate of
distance decay varies with the type of activity.
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Distance isnt as important as time and cost though when
determining the rate of distance decay. When the friction of
distance is reduced by lowered costs or increased ease of flow, the
slope of the distance decay curve is flattened and more total area
is effectively united.
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The Gravity Concept Interaction decisions are not based on
distance or cost considerations alone. Larger, regional shopping
centers (like a mall) attract more people because of the variety of
shops and goods that its size promises. You go to big cities to
seek your fortune, as opposed to the nearest small town. We are
attracted by the expectation of opportunity that we associate with
larger places.
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` Henry Carey: (1793-1879) wrote Principles of Social Science.
He observed that the physical laws of gravity and motion developed
by Sir Isaac Newton were applicable to the aggregate actions of
humans. Newtons law tells us that big things attract each other
more than do small objects, and things that are close have a
greater attraction then things at a distance, and that the
attraction decreases greatly with even the smallest increase in
separation.
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Carey was interested in the interaction between urban centers
and in the observation that a large city is more likely to attract
an individual than is a small hamlet. He took Newtons formula, and
exchanged physical mass for population size. Exchanges (E) AB =
Population of A * Population of B Distance between A and B
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In social (such as Careys work), rather than physical (Newton),
distance may be calculated by travel time or travel cost
modifications rather than by straight line separation We know two
things from this: 1. That exchanges decrease as one increase
distance from the source (in this case, an Urban area) 2. That in a
stationary place, exchanges will increase as the size of the source
increases.
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William J. Reilly: (1899-1979) Proposed the law of retail
gravitation in 1931 Reilly determined the relative amount of retail
trade that two cities would attract from an intermediate place in
the vicinity of the breaking point.
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What Reilly is saying is that any farm or small-town resident
that is located between the two bigger cities, would be inclined to
shop in one or the other according to that residents position
relative to the breaking point. | City A (pop 70k) BP Farmer M City
B (pop 150k) | | |
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The gravity model can be used to account for a wide variety of
flow patterns in human geography. Population migration Commodity
flows Journeys to work or to shop Telephone call volumes Etc
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Interaction Potential Distance decay models and gravitational
pull models only deal with two places In reality, the world is
rather more complex. All cities, rather than just two, in a region
have the possibility of interacting with each other. In addition to
that, the more specialized each city becomes, the greater their
collective complementarity, and the more likely that multiple
interactions will occur
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A Potential model, which is also based in physics, estimates
the interaction opportunities available to a center in such a
multi-centered network. It gives the relative position of each
point in relation to all other places within a region This model is
applicable whenever intensity of interaction is of concern;
Marketing Land values Broadcasting Commuting patterns, etc.
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Movement Biases Distance decay and the gravity and potential
models help us understand the bases for interaction in a perfect
world one with no natural or cultural barriers to movement. Once
flow patterns develop, they tend to cement themselves in i.e. A
shopping center attracts people, merchants see increased flow as
desirable and open new shops, so even more people go there to shop,
etc
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Such an aggregate regularity of flow as displayed by the
previous example is called a movement bias. We know of distance
bias, meaning people prefer short trips to long ones, but there is
also direction bias Of all possible directions of movement, actual
flows are restricted to only one or a few. Direction bias also
implies that from a given origin, movement is not random: In the
U.S., most tractor trailer flow is along an East- West axis, even
though from Kansas you could go any direction.
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Such directional biases, like the east-west flow of semi
movement in the United States, is a partial reflection of network
bias. Network bias is a shorthand way of saying that the presence
or absence of connecting channels strongly affects spatial
interaction. A set of routes and the set of places they connect are
called a network. This is not limited to moving goods, but also
information
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Everything we have talked about, especially these biases, move
us away from the three bases of spatial interaction and aggregate
behavior, and towards more individualized movements and behavior.
The questions we ask in terms of spatial interaction, lead us to
how much refinement we need.
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Human Spatial Behavior Mobility: term applied to all types of
human territorial movement. There are two types that concern us:
Daily or temporary use of space going to the store, work, school,
etc, as well as longer periods such as vacations or going to
college. Longer term commitment such as permanently leaving the
home and finding residence in a new location. The second type is
known as migration.
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Groups and countries draw boundaries around themselves, divide
space into territories, and defend them if necessary.
Territoriality: the emotional attachment to and the defense of home
ground. On a more individualized basis, we each claim personal
space, the zone of privacy and separation from others our culture
and physical circumstances require or permit.
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Besides having our home territory, we also have a home range,
known as activity space, an area in which we move freely on our
rounds of regular activity. The following map shows the probably
activities for a family of 5 for one day. Note: activities for the
group cover a small area, and individual, the area is even smaller.
Note: over a longer period of time, more paths would have to be
added, extending the area covered.
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The types of trips and thus the area of their activity space,
depend on at least the following three variables: Stage in life
course (age) The means of mobility at their command The demands or
opportunities implicit in their daily activities.
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The Tyranny of Time All of our activities consume time as well
as space. Your spatial reach is restricted because you cannot be in
two places at once. There is also a finite amount of time within a
day, and your spatial choices have to take this into account. Our
daily space-time constraints may be represented in a space-time
prism. Critical Distance: the distance beyond which cost, effort,
and means, strongly influence our willingness to travel.
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Since most activities have their own time constraints, the
choices of things you can do and the places you can do them are
strictly limited. Defined class hours, travel time from home to
school, among other things, may be constraints on your space- time
path. What jobs you can take are limited by what can fit within
your daily space time prism
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To the right is a Space- time path for a hypothetical college
student.
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Answer the following on a sheet of paper What is meant by
spatial interaction? What is activity space? What factors affect
the areal extent of an individuals activity space? Plot your
space-time path on a typical class day. What alterations in your
established movement habits might be necessary if (a) you rode a
bike instead of walked? (b) instead of riding a bike you drove a
car? (c) you had to take a bus instead of going by bike, foot, or
car?