Geographic conditions influence the economic and social development of a people by the abundance, paucity, or general character of the natural resources, by the local ease or difficulty of securing the necessaries of life, and by the possibility of industry and commerce afforded by the environment.

From the standpoint of production and exchange, these influences are primarily the subject matter of economic and commercial geography; but since they also permeate national life, determine or modify its social structure, condemn it to the dwarfing effects of national poverty, or open to it the cultural and political possibilities resident in national wealth, they are legitimate material also for anthropo-geography.
[Sidenote: Size of the social group.] They are especially significant because they determine the size of the social group.

This must be forever small in areas of limited resources or of limited extent, as in the little islands of the world and the yet smaller oases.

The desert of Chinese Turkestan supports, in certain detached spots of river-born fertility, populations like the 60,000 of Kashgar, and from this size groups all the way down to the single families which Younghusband found living by a mere trickle of a stream flowing down the southern slope of the Tian Shan.

Small islands, according to their size, fertility, and command of trade, may harbor a sparse and scant population, like the five hundred souls struggling for an ill-fed existence on the barren Westman Isles of Iceland; or a compact, teeming, yet absolutely small social group, like that crowding Malta or the Bermudas.