A new classification of 15 relief patterns at the global scale combines a relief roughness indicator and the maximum altitude at a resolution of 30 30. Classical geographic terms have been retained but assigned to fixed relief roughness (RR = maximum minus minimum elevation per cell divided by half the cell length in meters/kilometer, or and altitude boundaries. Plains (33.2 Mkm2 of currently nonglaciated land surface) correspond to subhorizontal terrain (RR 20). Plateaus (16.8 Mkm2), with mean elevations between 500 and 6000 m, have a medium degree of roughness (RR from 5 to 40). Mountains (33.3 Mkm2) are differentiated from hills by their higher mean elevation (>500 m) and from plateaus by their greater roughness (>20 then >40) in each elevation class. Accordingly, Tibet and the Altiplano are very high plateaus, not mountains. These quantitative definitions of relief patterns were divided into 15 classes, then clustered into 9 main types and mapped at the global scale at a resolution for which water runoff depth and population were previously determined. We also differentiated between exorheic areas (115.6 Mkm2 globally) and endorheic areas (17.36 Mkm2 globally) of potential runoff. Mountains thus account for 25% of the Earth's total land area, 32% of surface runoff, and 26% of the global population. The presence or vicinity of a rough and elevated landscape is less limiting to human settlement than water runoff.

[This publication is referenced in the "Synthesis of knowledge of extreme fire behavior: volume I for fire managers" (Werth et al 2011).]