What is the term for a straight line between start and finish positions or between waypoints?

The term that refers to a straight line between start and finish positions or between waypoints is a rhumb line. A rhumb line, or loxodrome, represents a path of constant compass bearing, meaning that you would maintain the same heading throughout your journey. This type of line crosses all meridians at the same angle, which is why it appears as a straight line when plotted on a typical Mercator projection map.

Understanding the concept of a rhumb line is important in navigation because it simplifies the process of plotting a course over long distances. While it is not the shortest distance between two points (which would be represented by a great circle), it is often more straightforward for navigators to follow.

The great circle is the shortest distance between two points on the surface of a sphere, but it does not usually represent a straight path when plotted on a standard map. A latitude line represents a circle of constant latitude, which runs east to west and is not typically associated with a direct course between two points. The term course line can denote the intended path of a vessel but is not specifically defined as a straight line connecting two points. Therefore, the correct identification of this term as a rhumb line is crucial for understanding navigation principles.