What does Chart Projections cover?
Map projections trade off which properties they preserve. Navigation relies mainly on the Lambert conformal and Mercator charts, and the exam tests their properties: how great circles and rhumb lines appear, and how scale and convergence behave.
What this subject covers
- Conformality and the idea of a projection
- Mercator: rhumb lines straight, scale expands with latitude
- Lambert conformal: great circles ~straight, used mid-latitudes
- Convergence and scale variation
Study tip
Memorise, per chart, how a great circle and a rhumb line each plot — that single fact answers a surprising number of questions.
Frequently asked questions
How does a great circle appear on a Mercator chart?
As a curve concave to the equator (convex to the nearer pole); the rhumb line, by contrast, is a straight line.
Why is the Lambert chart used for navigation?
Because at mid-latitudes a great circle plots almost as a straight line and scale is nearly constant, making it convenient for route plotting.
