Friday, February 25, 2011

Map Making

A map is a schematic representation of an area. Maps are primarily used to help locate places or plan a journey, and can range from a plan of a farm to a map of the world. Maps may also be used to illustrate information about a particular area; for example, distribution of population, resources or climate. These specialized maps are known as thematic maps.

                In any map the way reality is represented depends on the amount of information it contains, the used of diagrams and other graphic devices, and the scale- the size of the map in relation to the area it shows. The oldest surviving maps were made by the Babylonians more than 4000 years ago. Many ancient mapmakers assumed that the Earth was flat, but the circumnavigation of the globe in the 15th century led to great improvements in the accuracy of map making.  

                Maps show a range of information by the use of symbols and approximations. The first stage of map making is to construct a network of fixed points, from which everything else can be located. That way subsequent error will not accumulate and cause major distortions.  Before map makers had aerial photographs and satellite images to help them, the fixed points were plotted by a process called triangulation. Triangulation points are set up on landmarks such as hilltops. From the angles between these points, distance can be calculated without the need to take measurements on the ground. Adding vertical angle measurements give the heights. The height information on maps is normally shown as contours- lines linking points of the same elevation. It was by setting up a triangulation system across India from the coast to the Himalayas that cartographers first established the Mount Everest was the highest mountain in the world.  Today, satellite images provide the framework and maps are stored on computer so that they can be updated quickly without the need for redrawing.