## Assumed knowledge

- Familiarity with circle measurement formulae, including circumference and area
- Familiarity with trigonometric calculations, including basic SOHCAHTOA, sine and cosine rules
- Familiarity with area of triangles using sine area rule
- Familiarity with circle geometry.

## Motivation

- What have circles to do with measuring distances on the surface of the Earth?
- Do I have to use radians for measuring any angles?
- Will it make much difference to the distance calculated if I use an incorrect method?
- Why is the straight-line distance between two points on a sphere not necessarily the shortest distance between those two points?
- How does a spherical model of the Earth help me to understand the different time zones that have been established?

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