Distribution of Data - Spatial Mathematics: Theory and Practice through Mapping - page 185

pull from the high population of China and southeast Asian countries such
as Indonesia and Vietnam.
8.7.2 Standard deviational ellipse
Next, examine the directional distribution for the top 10 cities for each of
the years under study. This standard deviational ellipse measures whether
a distribution of features exhibits a directional trend (Figure 8.7). The
smaller the ellipse, the more clustered the top 10 cities are. If the spa-
tial pattern of the features is concentrated in the center with fewer cities
toward the edges, a one standard deviation ellipse covers 68% of the cities.
When was the ellipse the smallest, and why? The ellipse was smallest in
1900 as industrialization attracted migrants to and concentrated people in
large cities such as London, Paris, and New York City. What do you think
the standard deviational ellipse will look like in 2050 given the current
population trends? Many scenarios are possible, but it is likely that given
the increasing population in Brazil, Nigeria, the Middle East, and India, the
standard deviational ellipse will cover an even greater portion of the Earth
than today. It will also tend toward the south because northern countries in
Europe and also Russia experience slow growth and in some cases, popula-
tion decline.
Figure 8.7 Standard deviational ellipse. Source of base map: Esri software.