Spatial Analysis of U.S. Agricultural Distributions
INTRODUCTION
Location Factors
Location factors are characteristics of a place which influence where a
given phenomenon will be located. For example, the type of soil in
a given place will influence what type of agriculture, if any, could be
practiced successfully at that place. If a given characteristic is
not spatially differentiated (does not vary significantly from place to
place), then it would not be a location factor. For example, even
though air is required for agriculture, the amount (except for areas of
very high elevation) and quality (except for some very polluted areas that
may have excessive acid precipitation) of air does not vary enough over
the earth's land surface to be a deciding factor as to where most types
of agriculture can be practiced. The number of people in an area
would be a location factor influencing where various types of services
(such as retailing) could be successful.
Spatial Distributions
A spatial distribution is the location of phenomena across an area.
For example, where trees are located throughout a park would be the spatial
distribution of trees in the park. When geographers observe the spatial
distribution of a phenomenon they usually describe it in terms of density,
concentration, and pattern. Density is the amount of the phenomenon
per amount of land area, such as how many houses are located on each acre
of land. Concentration is an evaluation of the degree of dispersement
of the phenomenon within the area of study. For example, trees in
a park could be uniformly dispersed over the entire park, or they might
be concentrated in one grove of trees with the rest of the park covered
in grass. The pattern of a spatial distribution is the existence
of particular orderliness, such as the trees in the park being in linear
patterns bordering the streets and walkways in a park. Observing density,
concentration, and pattern of a particular distribution can give insights
into understanding the processes that gave rise to that particular distribution.
Spatial Correlation (Association)
Spatial correlation or spatial association is the concept of how related
the distributions of two different sets of phenomena are. For example,
the location of streets and street lights would obviously be correlated.
One seldom finds a street light where there are no streets. Shopping
malls are usually located near major street intersections, so they would
be spatially correlated or associated. There could also be "negative"
correlation. For example, one seldom finds aquaculture (such as catfish
farming) in desert regions. So, where one is found there is the absence
of the other; that's negative association. There are statistical
techniques for measuring spatial correlation, but a simple, valuable technique
is to visually compare two maps which show the distribution of the phenomena.
Created 6/20/97 by Charles T. Ziehr. Last updated April 24,
2000.
The URL for this page is http://arapaho.nsuok.edu/~ziehr/virtual/human_wg/agric/ag_intro.html