Currently widely used projections include Mercator Projection (normal conformal cylindrical projection), Gauss-Krüger Projection (transverse conformal cylindrical projection), UTM Projection (transverse conformal secant cylindrical projection), and Lambert Projection (conformal secant conical projection).
Mercator Projection
The Mercator Projection is a "conformal tangent cylindrical projection" developed by Flemish cartographer Gerardus Mercator in 1569. It assumes the Earth is enclosed in a hollow cylinder tangent at the standard parallel. Imagining a light source at Earth's center projects surface features onto the cylinder, which is then unwrapped to create the map.
This projection preserves angles without distortion, maintaining equal scale ratios in all directions from any point. Its meridians and parallels form a rectangular grid with constant meridian spacing and gradually increasing parallel spacing from the standard parallel toward the poles. While significant area distortion occurs away from the standard parallel, the uniform expansion preserves directional relationships, making it ideal for navigation charts.
The Mercator Projection's key advantage lies in preserving true directions. Navigators can follow straight-line rhumb lines between points while maintaining constant bearing. This property makes it indispensable for marine navigation and aerial charts.
Gauss-Krüger Projection
The Gauss-Krüger Projection, a "transverse conformal cylindrical projection", was initially developed by Carl Friedrich Gauss in the 1820s and refined by Johannes Krüger in 1912. It employs a cylinder tangent to a central meridian, projecting areas within specific longitude ranges onto the cylindrical surface while preserving conformality. The cylinder is then cut along generatrices and flattened.
Post-projection, only the central meridian and equator remain straight lines. This projection maintains angular accuracy with minimal scale distortion (≤0.1% within 250km of central meridian). Distortion increases toward zone edges, peaking at equator extremities. Its high precision and simplified zonal calculations make it essential for large-scale topographic mapping.
Zonal division effectively controls distortion:
- 6-degree zones: 60 zones numbered 1-60 from 0° longitude
- 3-degree zones: 120 zones numbered 1-120 from 1.5° longitude
UTM Projection
The Universal Transverse Mercator (UTM) projection, a "transverse conformal secant cylindrical projection", secures the Earth at 80°S and 84°N. Featuring 0.9996 scale factor at central meridian, it minimizes distortion to ≤0.04% within zones. Adopted by the U.S. Army in 1947, UTM divides the globe into 60 six-degree zones (180°W-180°E). Two standard meridians 180km from central meridian maintain true scale. Widely used for satellite imagery in China.
Lambert Projection
Lambert Conformal Conic Projection, developed by Johann Heinrich Lambert in 1772, uses a secant cone to project spherical coordinates. It preserves conformality with these characteristics:
- No angular distortion
- Equal deformation along parallels
- Zero distortion at two standard parallels
- Positive scale distortion outside standard parallels, negative between them
- Equal arc lengths along meridians between parallels
China's 1:1,000,000 topographic maps adopt this projection with 4° latitude zones. Each zone uses standard parallels offset 30' from sheet edges, enabling seamless east-west mosaics while requiring special handling for north-south joins across zones.
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