Marginal Distributions of Population and Land Area


The marginal distributions of the bivariate density functions shown in the previous figure. Both frequency histograms (filled bars) and empirical cumulative distributions (solid curves) are shown for (a) number of people by elevation; (b) occupied land area by elevation; (c) number of people by population density and (d) occupied land area by population density.

Marginal distributions of both population and occupied land area as functions of elevation and population density can be derived from the HAD and LAD (above). The marginal distribution of people as a function of population density reveals that 55% of the world's population lives at densities between 100 and 1000 people/km2. The number of people diminishes gradually as population density decreases below 100 people/ and drops rapidly as population density increases above 1000 people/ The marginal distribution of people as a function of elevation reveals that approximately 1.96 x 109 people, or 34% of world population, live within 100 m of sea level. At elevations > 800 m, log10 of population falls linearly with increasing elevation but at elevations below 800 m, log10 of population increases concavely upward. Thus globally, as elevation drops from 800 m towards sea level, the number of inhabitants increases faster than exponentially while the occupied (and total) continental land area increases almost linearly. Consequently, average population density increases with decreasing elevation below 800 m.

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