The characteristics of this widespread representation of Earth's surface
| A coordinate system used for locating any point on the surface of a sphere or spheroid is essential for any map projection. It provides scientists with a means by which they can systematically represent a spatial, surface-based phenomenon on the Earth's surface onto a flat plane, such as a map. The Cartesian coordinate system in geometry is a simple, easily recognizable example. This system has an origin, the point at which two initial perpendicular lines meet, and both lines extend in opposite directions to infinity. Along the lines, distance values increase in magnitude on a continuous linear scale away from the origin. In the case of the geographic reference system as used for objects like the Earth, the globe is divided horizontally into 360 units (called degrees), and vertically into 180 units. The "origin" is placed at a point along the equator (the line forming the maximum diameter of a spherical object around the perpendicular of its axis of rotation). As a result, negative coordinate values can be obtained south and west of this point, making the range of coordinate values from -180 degrees to +180 degrees from west to east (longitude), and -90 degrees to +90 degrees from south to north (latitude). Each degree is divided into 60 minutes, and each minute is partitioned into 60 seconds, although for most calculations, decimal degrees are easier to use. Thus, "120.5 degrees" is another way of saying, "120 degrees, 30 minutes." Shown here is the geographic reference system, otherwise classified as the standard Plate Carree projection. Notice that each 30-by-30 degree block (outlined by dark blue lines) is a perfect square. Although in reality the North and South Poles (+90 and -90 degrees, respectfully) are points on the Earth surface, they are displayed here as straight lines along the top and bottom of the map. Cartographers use a term called distortion to describe the level of how different a feature is shown compared to its true appearance, form or characteristic of a map. As a result, "high-latitude areas" (near the North and South Poles) are very distorted; in fact, the squares formed that touch the top and bottom of this map are actually triangular, wedge-shaped areas on the Earth! Unfortunately, only areas near the equator are shown without distortion. Many maps are represented showing this projection, because most scientific data is recorded with latitude and longitude, is easily plotted using this system, and can be mathematically transformed into other projections to display certain areas with minimal distortion. This reference system is absolutely essential for the production of every other derived projection. On its own, however, this map style is inconsistent in the four forms of distortion: area, absolute distance (measuring in meters or feet), non-cardinal direction (navigation), and feature shape (rivers and coastlines). |
Credit: Dylan Prentiss, Department of Geography, University of California, Santa Barbara
For more info: http://www.geog.ucsb.edu/~dylan/mtpe/geosphere/topics/map/geographic.html