The globe grid

Maps are geographers' primary tools of spatial analysis. All spatial analysis starts with locations, and all locations are related to the global grid of latitude and longitude. Since these lines of reference are drawn upon the spherical earth, their projection onto a map distorts their grid relationships. The extent of variance between the globe grid and a map grid helps tell us the kind and degree of distortion the map will contain.

The key reference points in the grid system are the north and south poles and the equator, which are given in nature, and the prime meridian.w hich is agreed upon by cartographers. Because a circle contains 360 degrees, the distance between the poles is 180 degrees and between the equator and each pole, 90 degrees. Latitude measures distance north and south of the equator (0°), and parallels of latitude run due east-west. Longitude is the angular distance east or west of the prime meridian and is depicted by north-south lines (called meridians) that converge at the poles.

The properties of the globe grid the mapmaker tries to retain and the map user should look for are as follows:

1. All meridians are of equal length, each is one half the length of the equator.

2. All meridians converge at the poles and are true north-south lines.

3. All lines of latitude (parallels) are parallel to the equator and to each other.

4. Parallels decrease in length as one nears the polee.

5. Meridians and parallels intersect at right angles.

6. The scale on the surface of the globe is everywhere the same in every direction.

Дата добавления: 2015-07-19