题型：阅读理解 题类：常考题 难易度：普通
上海市虹口区2019届高三上学期英语期末考试试卷
The purpose of a map is to express graphically the relations of points and features on the earth's surface to each other. These are determined by distance and direction. In early times distance was often expressed in units of time, for example “so many hours' march” or “a day's journey by river”, but such measurements gave more information about the relative ease of crossing the local terrain than they did about actual distance. The other element is direction, but for the ordinary traveller, whose main concern was “Where do I go from here?” and “How far away is it?”, the accurate representation of direction was not of primary importance. Partly for this reason, written itineraries (行程) for a long time rivaled maps. Even today, certain types of maps, for example, those showing railway systems, may make little attempt to show true directions. Similarly, obvious landmarks along a route were at first indicated by signs, realistic or conventional (惯常的), and varied in size to indicate their importance. Clearly the conventions employed varied with the purpose of the map, and also from place to place, so that in studying early maps the first essential is to understand the particular convention employed.
The history of cartography (制图) is largely that of the increase in the accuracy with which these elements of distance and direction are determined and in the comprehensiveness of the map content. In this development, cartography has called in other sciences to its aid. For example, instead of determining direction by observing the position of a shadow at midday, or of a constellation (星座) in the night sky, or even of a steady wind, use was made of terrestrial magnetism (地磁学) through the magnetic compass, and instruments were evolved which enabled horizontal angles to be calculated with great accuracy.
The application of astronomical concepts, and the extension of the knowledge of the world through exploration, encouraged attempts to map the known world. Then astronomers discovered that the earth is not a perfect sphere, but is flattened slightly at the poles, which introduced further refinements into the mapping of large areas. Meanwhile, the demands being made of the map maker were shifting significantly. The traveller or the merchant ceased to be the sole user of maps. The soldier, especially after the introduction of artillery, and the problems of range, field of fire, and dead ground which it raised, demanded an accurate representation of the surface features, in place of the earlier conventional or pictorial delineation (描绘), and a solution in any degree satisfactory was not reached until the contour (等高线) was invented.
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