Hypsographic demography: the distribution of human population by altitude

Abstract

The global distribution of the human population by elevation is quantified here. As of 1994, an estimated 1.88 x 10(9) people, or 33. 5% of the world's population, lived within 100 vertical meters of sea level, but only 15.6% of all inhabited land lies below 100 m elevation. The median person lived at an elevation of 194 m above sea level. Numbers of people decreased faster than exponentially with increasing elevation. The integrated population density (IPD, the number of people divided by the land area) within 100 vertical meters of sea level was significantly larger than that of any other range of elevations and represented far more people. A significant percentage of the low-elevation population lived at moderate population densities rather than at the highest densities of central large cities. Assessments of coastal hazards that focus only on large cities may substantially underestimate the number of people who could be affected.

Figure 1

(Left) Joint distribution of human population by elevation and population density, or Human Altitude Density (HAD), as a contour map. Contour lines show log₁₀(people). Example: the contour curve on the left that is labeled 8 passes through combinations of elevation and population density where about 10⁸ people live. Horizontal bin size is linear in elevation with a linear increment of 100 m, and vertical bin size is linear in log₁₀(people/km²), with each bin covering a constant factor of 10^0.25 (= 1.78) in population density. Thus 4 vertical bins span a 10-fold increase in population density. (Right) Joint distribution of land area by elevation and population density, or Land Altitude Density (LAD), as a contour map. Contour lines show log₁₀(land area (in km²)). For example, there are about 10⁶ km² of occupied land at each combination of elevation and population density through which the contour curve on the left that is labeled 6 passes. In both distributions, the values falling outside the bounds of the histogram are accumulated in the peripheral bins.

Figure 2

Marginal frequency histograms (filled bars, left ordinates) and cumulative distributions (solid curves, right ordinates) of number of people by elevation (a); occupied land area by elevation (b); number of people by population density (c); and occupied land area by population density (d). Derived from Fig. 1.

Figure 3

IPD (summed people divided by summed km²) by elevation.

Figure 4

Location of land at elevations ≤500 m (Top), >500 m and ≤1,500 m (Middle), and >1,500 m (Bottom), shown by the centroids of the 19,032 polygons in each elevational zone.