Lab 6- Map Projections

A map projection is a method of representing the Earth's 3D surface on a flat surface. They show various perspectives of the Earth and its features in order to better help people visualize the world in its entirety or smaller, distinct regions and landforms. Maps are constructed for specific purposes, but each projection chosen to preserve aspects of the Earth to serve that purpose simultaneously compromise other metric properties in order to achieve that goal. If a conformal map, for example, preserves the right angles of intersection between lines of longitude and latitude giving a more accurate direction or bearing, it cannot also maintain accurate shapes or areas of countries, and vice versa. One of the most popularly used projections is the WGS 1984; it uses spheroidal coordinates from the Geographic Coordinate System anchored at Earth's center, and provides the most concise global datum for defining surface locations. Using this map as the foundation in the lab, it gives the most true distance from Washington D.C., USA to Kabul, Afghanistan as 7012.543 miles.

Conformal maps, as previously mentioned, keep 90 degree angles at intersections, thereby creating a precise grid from which accurate directions and bearings can be measured. Two such maps are the Mercator and Gall Stereographic. On both maps, angles are preserved, but moving away from the mid-latitudes towards the poles, country shapes are distorted, stretched vertically, and the North and South Poles cannot even be shown. The Mercator, due to its gridded structure, can correctly demarcate local or regional areas and is used to generate bearing while in the air or at sea. It, however, entirely overestimates the measured distance between D.C. and Kabul by almost 3100 miles. The Gall Stereographic, having slightly less distrortion upon moving north or south from a varied false easting and northing, comes very close to the true distance, with a measurement of 7153.787 miles, which is impressive since its typical function is to display all countries on a single map, which leads to shape distortion and possible distance incongruence.

If, like most of the general public, someone just wants a planar map to show them countries or regions, an equal area map is a better fit. The Bonne Map is an equal area projection commonly used to portray single continents or smaller regions. A true scale remains along the central meridian and all parallels, which maintains an accurate sizing, but distortion does increase as objects move away from the Equator. Although the size of both the United States and Afghanistan are accurate in proportion to each other, and as they would be in 3 dimensional reality, Bonne only registers the distance between the 2 cities as 6738.138 miles. The Sinusoidal Equal Area Projection recorded a distance of 8107.158 miles. It, like the Bonne, represent single land masses well, but the Sinusoidal is most accurate in regions near the Equator. It has straight latitude lines and longitude lines curved based on sine functions, which distorts angles and distance as the parallels are spaced farther apart closer to the midlatitudes.

The last major "property-preserving" projection category is the equal distance map. The Conic variation has all circular meridians spaced evenly along meridians, making distance spacing equal. The poles are shown as arcs since shape and area distortion increase moving farther from the standard parallel. While it is best used to map midlatitude countries with a large east-west extent, it has provided the closest measurement to the WGS84 number with 6964.052 miles, roughly 18 miles variation. The second equal distance projection is Cylindrical. This projection uses simple calculation to form a grid of rectangles of equal size, shape and area. Distortion does increase as one moves away from the standard parallel, but there is less at the poles. Because of the grid, distance remains equal, though slightly skewed. But it is still only most accurate for local and city maps, indicated by 5023.934 mile city to city measurement.

All in all, choosing a map projection should rely on the desired intent of the map. Preserve the properties most integral to the topic of importance for the map's audience. In this experiment, the Conic Equal Distance projection proved to most accurately coincide with the measurements taken on the WGS 1984 datum map. While it seems that is an obvious choice because its function is to maintain correct distances, the Gall Stereographic, which preserves angles, came in a close second. Accuracy can be based not only on the metric properties preserved by the map overall, but by the location of points of interest. If the measurements had been of a region within the lines of the Tropics, a conformal projection may have been more reliable. But each projection is an estimation regardless, since different distortions are found in different areas throughout the map because a 2D projection can never measure up to the 3D reality.