How Maps Depend on the Earth's Form and Motions.—The shape and movements of the earth and its relation to the sun are of primary importance not only in determining latitude, longitude, time and the seasons, but in determining how maps shall be made. If there were no equator and poles, and if the earth's rotation did not cause the sun and stars continually to move through the heavens, there would be no such thing as locating points by means of observations of latitude and longitude. Because of the earth's rotation an explorer in Central Africa with his sextant and chronometer can put a newly discovered town on the map with a high degree of accuracy in an hour. If the earth did not rotate and were of irregular shape the only way to make maps would be by direct measurements from some center, such as London. Accurate measurements, however, would cost hundreds of dollars per mile by land, and would be almost impossible by sea. Thus, the accuracy and completeness of the art of mapmaking depend directly on the earth's form and motion.
Why Maps are Important.—It is impossible to study geography intelligently without maps. The primary purpose of maps is to show location. It is easy to say that a large city is located approximately in north latitude 30° and west longitude 90°, that it is on the Missis sippi River 107 miles from its mouth, close to Lake Pontchartrain, and that it is 140 miles southetest of Mobile and 165 south of Jackson, Mississippi. But how vastly easier it is to look at a map and see at a glance the relation of New Orleans not only to the mouth of the Mississippi, Lake Pontchartrain, Mobile, and Jackson, but to hun dreds of other rivers, towns, mountains, bays, gulfs, and other geo graphical features. Thus a map is chiefly useful because it shows the location of a great many features and their relation to one another both in distance and direction. In fact, under the heading " location " in Fig. 1, page 3, maps are by far the most important item. We fully realize their importance only when we are in circumstances like those of prisoners in Germany, for example, during the Great War. At that time maps were so important to any man who wished to escape that prisoners made little maps on their finger nails, inside their shoes, or in almost any place that they thought would not be noticed by their German guards. Even these inadequate maps helped them to find their way out of Germany when they had escaped from prison.
What Can be Shown on Maps.—Although the purpose of all maps tO 'gib* Jocation, they are equally useful in showing any of the other items of ;the table of Fig. 1. For instance, almost every
one is familiar with relief maps which show land forms by means of hachures, shading, contour lines, or colors. Most maps show lakes and rivers, but maps of minerals and soils are less common, although they are used by every intelligent mining man, and by many of the most up-to-date farmers. In the same way climatic maps are very common. Each day the Weather Bureau gets out a map showing the atmospheric pressure, winds, temperature, and cloudiness for the whole United States. By studying the weather map wide-awake firemen in large buildings save thousands of tons of coal. Many a mariner, fruit raiser, and shipper studies these maps with the greatest care, for he knows that his profits may be destroyed if he reads the map incorrectly.
Other conditions, such as the distribution of plants or animals, can readily be put on maps, as can every one of the human responses in the table of Fig. 1. Such maps may tell where fishing is the pre vailing mode of life, for example; the location of banana plantations; where people live in adobe houses, or wear wooden sandals instead of leather shoes. They may also show where people have much energy, where influenza is most common, where cotton goods are manufactured, where caravans are used most largely in transporta tion, where coal is an important article of commerce, where people worship idols, where democratic forms of government prevail, where baseball is a favorite recreation, and where civilization is high.
How Maps Help Explain Geographical Distribution.—In the pre ceding paragraph examples have been given of maps pertaining to each of the elements of geographical environment and many of the human responses as given in Fig. 1. Notice that in every case something is said about location or else the word " where " is used. That word furnishes the key to the value of maps. But to know where anything is located is not enough; we must also know why. Many times we can determine why by comparing one map with another, and such comparisons are one of the most important features of human geography. Only by a comparison of maps showing density of population and rainfall, for example, can we clearly under stand how great a diminution of population results from too little rain. Even the best maps, however, cannot explain many of the most interesting responses of man to his geographical environment, and for these we must rely on the accounts of travelers, on tables of statistics, and on many other sources.