Practical guide and verification
The arithmetic midpoint
For two numbers a and b, the midpoint is (a + b) ÷ 2. It is the value equally distant from both endpoints on a number line.
Coordinate midpoint
For points in a Cartesian plane, average each coordinate separately. That gives the midpoint of the straight line segment in that coordinate system.
Common mistake
A geographic midpoint on the Earth is not always the same as averaging latitude and longitude, especially across the antimeridian, near the poles, or over long distances.