THE SUBJECT MATTER OF GEOGRAPHY Classification and Content of Geography.—So complex a science demands the labour of many specialists in order to advance it by the separate study of its interdependent parts. There is a geographical aspect of all the sciences which are concerned with the earth and its phenomena and it follows that some knowledge of each of these sciences is required of the geographer in dealing with his proper subject. Though one aspect of geography merges into and is interwoven with another, lines must be drawn to allow of a classification for practical purposes. Each division of geog raphy draws its data from some source which is no longer viewed as essentially geographical but is known as one of the abstract or natural or human sciences, and on the other hand each division of geography is capable of practical applications in the arts or inter ests of civilized life. The degree of subdivision of the subject matter of geography varies according to the share of attention which each has received, but the main divisions, now recognized, are four : mathematical, physical, biological and human.
This deals with dimensions, fig ure and movements of the earth. Astronomical geography is a name sometimes given to the determination of position on the earth's surface by reference to the heavenly bodies and naviga tion is a practical application, the data of which are compiled in the British Nautical Almanac and similar publications of other governments. The earth's surface can be truly represented on a small scale only on a sphere and the terrestrial globe showing the degree net or lines of latitude and longitude is an essential geo graphical instrument. To represent the degree net, on a flat sur face or map, mathematical projections are necessary and these must be of various kinds to suit different purposes as every pro jection necessarily distorts the form or the area of any portion of the surface of the globe. The part of mathematical geography dealing with the size and figure of the earth is Geodesy which de pends on astronomical positions and the exact determination of distances on the surface by triangulation from bases which are directly measured. Geodetic operations do not necessarily do more than fix the degree net on the sphere, the process of topo graphical surveying serving to fill in details for maps on various scales, the production of which is the art of Cartography. Maps are adapted for the representation of any uniformly-varying dis tribution by the use of isopleths, of which the most familiar forms are contour-lines and isotherms, and by the use of conventional signs and distinctive colouring. Mathematical geography has also to do with the phenomena of the tides and of terrestrial mag netism while mathematical methods are essential in many depart ments of physical geography and in the treatment of all statistics distributionally. The figure of the earth is very nearly a spheroid of revolution, the equatorial radius of which measures 20,926,200 feet and the polar radius 20,854,900 feet, while a degree of latitude crossing the equator measures 362,745 feet and one crossing the pole 366,48o feet. The whole superficial area of the earth is approximately 196,940,000 square British statute miles.
The words "physical geography" have often been loosely used as equivalent to Physiography or the description of all nature. Here they are taken to mean the descrip tion of the forms of the lithosphere at their present stage of development and of the functions which these forms exercise in controlling the action of solar energy in the hydrosphere and at mosphere. The origin of the forms themselves and their relations to living creatures are excluded except incidentally for purposes of classification. It is evident that a physical geography is possible at any point of time in the life-history of the world during the un ceasing process of development by the powers tending simultan eously to increase the differences of level in the lithosphere, by stresses set up in it as it cools, and to decrease these differences by solar energy acting through air and water so as to cut down the heights and fill up the hollows. Physical geography falls into three divisions all depending on the laws of geophysics, viz.— Geomorphology or treating of the forms of the lithosphere depend ent in a special degree on geology; Oceanography or the conditions of the hydrosphere depending in a special manner on chemistry and physics; and Climatology or the condition of the atmosphere with respect to the earth's surface, depending largely on meteor ology. Attention is concentrated here on geomorphology as clima tology and oceanography are dealt with in special articles.
