几篇与机经相关的阅读文章。。。。

几篇与机经相关的阅读文章。。。。,标签：雅思阅读评分标准与雅思阅读真题下载,http://www.xuehuiba.com

　　World map in Mercator projection by van Keulen， about 1720. The ultimate map for navigation of the world， as first devised by Mercator （1569）。 On this projection， all straight lines are true bearings. This results in great size distortion toward the poles， which cannot be shown. Taken from Whitfield （1994， p. 108-109）。 Click on small image to see full-sized （148 kb） version.

　　Modern Maps

　　Maps became increasingly accurate and factual during the 17th， 18th and 19th centuries with the application of scientific methods. Many countries undertook national mapping programs. Nonetheless， much of the world was poorly known until the widespread use of aerial photography following World War II. Modern cartography is based on a combination of ground observations and remote sensing.

　　Map of the Danish Kingdom， 1629， by Janssonius. A high level of geographic accuracy is demonstrated along with marginal illustrations that enhance the map. Reproduction of original map from the Geodetical Institute of Denmark. Click on small image to see full-sized （184 kb） version.

　　Hondius' world map in two hemispheres， 1630， the quintessential Renaissance map. Taken from Whitfield （1994， p. 75）。 Click on small image to see full-sized （187 kb） version.

　　Geographic information systems （GIS） emerged in the 1970-80s period. GIS represents a major shift in the cartography paradigm. In traditional （paper） cartography， the map was both the database and the display of geographic information. For GIS， the database， analysis， and display are physically and conceptually separate aspects of handling geographic data. Geographic information systems comprise computer hardware， software， digital data， people， organizations， and institutions for collecting， storing， analyzing， and displaying georeferenced information about the Earth （Nyerges 1993）。

　　What is a Map？

　　Are maps realistic representations of the actual world？ No——never！ Field measurements are subject to errors of accuracy and precision. Aerial photographs and satellite images portray only certain portions of the light spectrum， as filtered through the atmosphere and detection instruments. No map can depict all physical， biological， and cultural features for even the smallest area. A map can display only a few selected features， which are portrayed usually in highly symbolic styles according to some kind of classification scheme. In these ways， all maps are estimations， generalizations， and interpretations of true geographic conditions.

　　All maps are made according to certain basic assumptions， for example sea-level datum， which are not always true or verifiable. Finally any map is the product of human endeavor， and as such may be subject to unwitting errors， misrepresentation， bias， or outright fraud. In spite of these limitations， maps have proven to be remarkably adaptable and useful through several millennia of human civilization. Maps of all kinds are fundamentally important for modern society.

　　The fool's cap world map， about 1590. Ptolemaic projection on the face of a clown. Maker， date and place of publication are unknown. Maps are human representations of the world， as seen through the eyes of a fool in this example. Taken from Whitfield （1994， p. 78-79）。 Click on small image to see full-sized （163 kb） version.

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