Spatial Interaction
Spatial interaction is a dynamic flow process from one location to another. It is
a general concept that may refer to the movement of human beings such
as intraurban commuters or intercontinental migrants but may also refer to
traffic in goods such as raw materials or to flows of intangibles such as
information. While the origins of the term may be traced to French geographers
of the early twentieth century, Edward Ullman’s “Geography as Spatial
Interaction” is normally cited as the seminal statement of the concept.
In Ullman’s conception there were “three bases for spatial interaction” or more
fundamentally, three reasons for why things move:complementarity,
transferability, and intervening opportunity.
Complementarity refers to the presence of a demand or deficit at one location
and a supply or surplus at another without which there is no economic rationale
for any movement. A workplace such as a factory or office tower is an example
of a place with a demand for labor while a residential neighborhood provides a
source of workers. A sawmill requires logs while a forest provides them. To
adapt a metaphor from physics,complementarity is like a potential gradient
with goods and people flowing from a higher energy state where they are in
surplus to a lower energy state, where they are in deficit. From the realm of
physical geography, wind is the flow of air between complementary
atmospheric zones: from a high pressure cell to a low pressure cell.
The complementary surplus-deficit relationship is commodity-specific,
and if the deficit is precisely specified, the direction and distance of movement
will depend on the location where there is a surplus of just that kind of good.
Complementary relationships may be the impetus for interaction between
distant regions such as the flow of petroleum over thousands of miles from the
Middle East to Europe and within regions such as the flow of shoppers from
residential neighborhoods to small convenience stores over a distance of less
than a mile or two.
David Ricardo’s classical economic concept of “comparative advantage”
provides a relative measure of the degree of
economic complementarity between two countries based on their opportunity
costs. All other things being equal, one nation will export goods to another
nation when it can produce a unit quantity at a lower relative cost than the
importing nation. In a similar vein, John Dunning’s eclectic theory of foreign
direct investment predicts that foreign investment will take place when a firm
in one country has such a powerful “firm-specific advantage” that it can
overcome the barriers to entry in a foreign country market in which there is a
“location-specific advantage” in factor costs such as land, labor or capital. Thus
foreign direct investment flows from regions with a surplus of capital to regions
with a capital deficit, creating the international ownership lineaments that
make-up the multinational corporation.
Transferability refers to the cost of overcoming distance measured in
real economic terms of either time or travel cost. The cost of overcoming
distance is known as the “friction of distance.” If the friction of distance is too
great, interaction will not occur in spite of a complementary supply-demand
relationship. Friction of distance depends on prevailing transportation
technology and the price of energy. In general, the friction of distance has
decreased over time which is the prime factor in globalization and the
emergence of megacities. Daily commuter flows, for example, are always
subject to a travel time constraint with two hours being a typical maximum for
the one-way daily journey to work. High-value, low-weight goods such as
jewelry are imminently transferable and exported on a global scale while
heavy, low-value goods such as concrete blocks are usually used very close to
where they are produced.
Intervening opportunity is the third basis for interaction although it
typically is considered as the reason for a lack of interaction between two
complementary locations. Complementarity will only generate a flow if there is
no intervening, or closer, location. The flow of goods that would otherwise
occur between two complementary; locations may be diverted to a third
location if it represents an intervening opportunity: a closer complementary
alternative with a cheaper overall cost of transportation.
However, Ullman noted that the trade diverting effect of an intervening
opportunity could eventually facilitate interaction between more distant
complementary locations. In his example, the nearest (intervening) source of
logs would justify construction of a short logging railway from the mill to the
forest resource and when it was harvested, the railway would be extended to the
next intervening opportunity and so on until it ultimately reached a more distant
complementary location. Flows to the more distant complementary location
might never have been established had the transportation infrastructure not
been constructed in a series of incremental extensions to a series of intervening
opportunities.
Important forms of spatial interaction such as traffic flows and migration may
be predicted and explained based on an analogy with Newton’s model of the
gravitational attraction between celestial bodies. Assuming that there is no
intervening opportunity, the degree of complementarity between any two
regions is proportional to the product of the populations of the origin and
destination regions and inversely proportional to the distance between them,
representing transferability. Thus the level of spatial interaction may be
specified as:
where Tij is the spatial interaction between origin i and destination j,
Pi and Pj are their respective populations, dij is the distance between them,
and b is an exponent representing the interaction retarding effect of the friction
of distance which depends on transportation technology. To calibrate this
simple model, a constant, k, is introduced to account for scale differences.
The concept of spatial interaction can be traced to French geographers’
notions of géographie de circulation, including both the movement of physical
objects and the communication of intangible ideas. But its fullest development
as the most fundamental of all geographic concepts came in the middle 1950s
as the seminal contribution of Ed Ullman. Hitherto, geography had been
conceptualized as a way of describing the arealdifferentiation of sites. With the
spatial interaction concept, Ullman shifted attention to situation as a second and
equally important locational attribute. Areal differentiation emerged as the
outcome of transportation and trade which permitted specialization in particular
economic activities and concentrations of various social groups. Thus spatial
interaction remains fundamental to understanding the development of
distinctive regional geographies.
Activity Space
the space within which daily activity occurs
Awareness Space
knowledge of opportunity locations beyond normal
activity space
Chain Migration
migration of people to a specific location because relatives
or members of the same nationality previously migrated
there
Complementarity
the actual or potential relationship between two places,
usually referring to economic interactions
Counter Migration
the return of migrants to the regions from which they
earlier emigrated
Critical Distance
the distance beyond which cost, effort, and/or means play
a determining role in the willingness of the people to
travel
Distance Decay
the effects of distance on interaction, generally the greater
the distance the less interaction
Friction of Distance
The increase in time and cost that usually comes with
increasing distance.
Gravity Model
A mathematical formula that describes the level of
interaction between two places, based on the size of their
populations and their distance from each other.
Intervening Opportunity
the presence of a nearer opportunity that greatly
diminishes the attractiveness of sites farther away
Law of Retail Gravitation
law that states that people will be drawn to larger cities to
conduct their business because larger cities have a wider
influence on the hinterlands that surround them
Migration
the movement of persons from one country or locality to
another
Mobility
all types of movement from one location to another
Movement Bias
any aggregate control on or regularity of movement of
people, commodities, or communication. (Included are
distance bias, direction bias, and network bias.)
Network
A set of routes and the set of places that they connect
Personal Communication Field
An area defined by the distribution of an individual's
short-range informal communication. The size and shape
of the field are defined by work, recreation, school, and
other regular contacts and are affected by age, sex,
employment, and other personal characteristics.
Personal Space
The zone of privacy and separation from others our
culture or our physical circumstances require or permit
place perception
..., the awareness we have, as individuals, of home and
distant places and the beliefs we hold about them
Place Utility
is the measure of an individual's satisfaction with a given
residential location
Potential Model
provides an estimate of the interaction opportunities
available to a center of a network
Pull Factor
factor such as freedom or employment opportunities that
attract a person to a country
Push Factor
factor that induces people to leave old residences
Reilly's Law
two cities will attract trade from intermediate locales in
direct proportion to the populations of the two cities and
inversely proportional to the square of the distance of the
two cities to the intermediate place (law of retail
gravitation)
Return Migration
the voluntary movements of immigrants back to their
place of origin. Also known as circular migration
Space-time prism
the volume of space and length of time within which our
activities must be confined
Spatial Interaction
the movement of people, goods and ideas within and
across geographic space
Spatial Search
the process by which individuals evaluate the alternative
locations to which they might move
Step Migration
migration to a distant destination that occurs in stages, for
example, from farm to nearby village and later to a town
and city
Territoriality
our sense of ownership of space that remains fixed
Transferability
the ease (or difficulty) in which a good may be transported
from one area to another.