From the last
lecture, we noted that economic activity concentrates in cities because
of a variety of external economies — benefits that increase the value of
city locations to all users.
While there are
also external diseconomies of agglomeration (such as the costs of
congestion, which are greater for the place overall than they are for the
individuals who cause the congestion), cities persist as long as the economies
are
greater.
What determines the location
of cities?
TRANSPORTATION ROUTES, especially
naturally provided rights-of-way like rivers and ocean harbors, reinforced
by expensive human-produced rights-of-way like major rail routes
SPECIALIZED FUNCTIONS, such as mining
or natural-resource oriented manufacturing, that need to be in a particular
place and that employ people who in turn need services
RELATIONSHIP TO OTHER SETTLEMENTS,
since two very large cities are not likely to survive very close together.
Why is this? Why is there a tendency for large cities to be separated by smaller cities, and smaller cities to be separated by towns and villages?
In addition to port and manufacturing functions, most settlements serve as central places: places where goods and services are exchanged (for money), usually attracting local residents to staff the markets and provide services. They provide these market and service functions for a surrounding area, called a hinterland. (Think about the agricultural region whose land prices are determined by the distance to the market center).
This way of looking at the world would expect a set of settlements of
about the same size, each serving as a central place for an agricultural
hinterland. The fact that some settlements also have port, transport,
and manufacturing functions will make some places larger than others.
What else makes some
places larger than others?
Some goods and services can be provided at a small scale, for a small,
localized market (grocery stores, barber shops, gas stations). But
some goods and services require larger market areas —
The threshold of a good (or service) is the minimum service area or hinterland required to contain enough people to support the provision of the service: smaller for inexpensive, every-day, lower-order goods and services; larger for expensive, seldom-purchased, higher-order goods and services. See pages 247-250 of the Hanink text.
We also can speak of the range of a good or service: the maximum distance that most people will travel to buy the good or consume the service.
Note that the area represented by a threshold varies with the density of population, while the range is a distance. In areas with very sparse population, it’s conceivable that some goods won’t be offered at all: the threshold required for providing the service is greater than the range for enough people to support it.
Some central places, high-order central places, contain a full
range of goods and services, and serve large hinterlands. Some points
in such a large hinterland are too far from the central place for it to
be their source of low-order goods: the range of those goods is not
large enough for many people to travel a long distance to consume them.
Other central places, low-order central places, provide relatively
few goods and services, and serve small hinterlands. Their hinterlands
will also be the hinterlands for some high-order central place, from which
residents will obtain high-order goods and services.
(See Hanink, pp.283-8).
This gives us a nested hierarchy of hinterlands
and central places. Each hinterland is theoretically a circle around
a given central place. [note drawing in class]
However, adjacent circles do not fill a two-dimensional space [illustrate
in class]. The best way to fill a two-dimensional space, with the
minimum number of polygons, is to use hexagons. [draw hexagons]
Nesting these hinterlands would give us a pattern
of lower-order central places in the corners of the hexagons of the higher-order
hinterlands. [Figure 7.11 in the S&deS text]
The overall pattern of central places and their hinterlands would look
like Figure 7.12 in the S&deS text [transparency in class].
There are 3 times as many central places of one order as there are central
places of the next higher order; which is to say that the hinterlands
of one order of central place is three times the size of the hinterlands
of the next-higher-order place.
We call this a k = 3 hierarchy.
Recognizing the utility or likelihood that the lower-order central places will actually thrive along the transport routes that link higher-order places, a more realistic pattern is to arrange the lower-order centers in this way, as in Figure 7.13b in the S&deS text. This yields 4 times as many central places of one order as there are central places of the next higher order. We call this a k = 4 hierarchy.
Of course, this theoretical pattern of central places (also called CENTRAL PLACE THEORY -- a theory of city formation and location as a function of their roles as central places) is not the only determinant of the location of cities. As we noted at the outset, cities’ locations are also determined by major transportation facilities such as natural harbors, navigable rivers, and the presence of flat, dry land with some fresh water available. In addition, the location of a key natural resource or manufacturing activity may determine the location of a city.
However, these other
reasons for city location merely skew the natural inclination to a nested
hierarchy of large and small cities.