Map Projection Fundamentals

Study Notes

Map Projection Fundamentals

Map Projection: A method to represent the curved surface of the Earth onto a flat surface.
Graticule: A network of parallels (lines of latitude) and meridians (lines of longitude) displayed on a map, representing the Earth's grid system.
Generating Globe: A model of the Earth used as a reference for creating projections. It's often a wire or glass globe.
Developable Surface: A geometric shape onto which the Earth's surface is projected. Common surfaces include cones and cylinders.
Cone Projection Examples:
- Conical Projection with one standard parallel
- Conical Projection with two standard parallels
- Bonne's Projection
- Polyconic Projection
Cylindrical Projection Examples:
- Cylindrical Equal Area Projection
- Cylindrical Equi-Distant Projection
- Mercator's Projection
Standard Parallel: The parallel of latitude where the developable surface touches the generating globe. The scale is most accurate along this parallel.
Central Meridian: The central meridian on which the radial scale (scaling in a straight line outward from the central meridian) is accurate. Distortion increases further from the central meridian.
Constant of Cone: This value relates the angle at the vertex of a cone to the angle of the pole on the generating globe, and it helps define the conical projection. The formula is: Constant of Cone (n) = α/360, where α is the angle of the cone's vertex.
Scale Factor: The ratio between the map's scale and the real-world scale, or the ratio of a distance on the map to the actual distance on the ground.

Types of Scale Factors

Tangential Scale Factor (TSF): Compares the length of a parallel of latitude on the globe to the length of the same parallel on the map.
Radial Scale Factor (RSF): Compares the length of a meridian on the globe to the length of the same meridian on the map.

Datum & Geoid

Datum: A reference surface that defines the position of points on the Earth. The most common datum is the World Geodetic System 1984 (WGS-84), which is based on the mean sea level.
Geoid: The actual shape of the Earth, which is an irregular, slightly flattened sphere.

Orthodrome & Loxodrome (Great Circle & Rhumb Line)

Great Circle (Orthodrome): The shortest distance between two points on the surface of the Earth. On a great circle, the compass bearing changes constantly.
Rhumb Line (Loxodrome): A line that intersects all meridians at a constant angle. On a rhumb line, the compass bearing remains the same. Loxodromes appear as straight lines on Mercator's Projection.