What is a rhumb line?

Question

In relation to a line drawn between the base of the uprights holding the bar over which a competition pole vault is being made, where is the box situated in which the pole is planted?

Answer 1

A navigational aid
It marks out a path with constant bearing as measured relative to true north, a line on the surface of the earth that follows a single compass bearing and makes equal oblique angles with all meridians . It appears as a straight line on a Mercator projection chart.