Map Projections and Gnomonic Projection

Map Projections

• Cartographers use various techniques to create maps that accurately represent the Earth's surface on a flat plane.
• Different projections preserve different aspects of maps, like angles, shapes, or distances.
• Common projections include Gnomonic, Mercator, and Conic.

Gnomonic Projection

• Displays great circles as straight lines, showing the shortest route between two points.
• Created by projecting points of a sphere onto a tangent plane.
• Distortion increases exponentially away from the tangent point (center of the map).
• Preserves angles (azimuthal projection) from the tangent point.
• Used for seismic work (seismic waves travel along great circles), photography (rectilinear projection), and star charts/astronomy (meteor paths).
• A great circle is also called an orthodrome; the largest circle that can be drawn on a sphere.
• Considered the oldest projection type, developed in the 6th century BCE for star charts.
• "Gnomonic" relates to sundials or telling time.
• Significant distortion away from the central point, making countries appear distorted in shape farther away.

Mercator Projection

• Conformal, cylindrical projection using longitude and latitude lines.
• Longitude lines are parallel and equally spaced meridians.
• Latitude lines are perpendicular and become farther apart near the poles.
• Preserves angles and shapes at an infinitesimal scale, so a straight line equals a compass bearing.
• Represents a globe wrapped in paper.
• Created by Gerardus Mercator in 1569.
• Originally designed for accurate compass bearings for sea travel.
• Distorts size to preserve shape, particularly problematic near the poles.
• Useful for large-scale maps of areas near the equator and for standard sea navigation charts.
• Often used in web maps and online services.

Conic Projection

• Projects images onto a cone.
• Projection is along a line of latitude (called the standard parallel).
• Meridians project across the cone.
• Latitude lines are projected as rings on the cone.
• Cone is cut, creating the final map.
• Distortion increases away from the standard parallel.
• Useful for midlatitude regions or maps of smaller portions of the Earth.
• More complex projections (secant projections) use two standard parallels.
• Commonly used for maps with east-west orientation.
• Suitable for road maps, weather maps, and smaller regions.