Rene Descartes invented the Cartesian coordinate system in the 1600s while observing a fly crawl on his ceiling. He realized he could describe the fly's position using its distance from the walls of the room. The coordinate system specifies each point uniquely in a plane using a pair of numerical coordinates representing the signed distances from the point to two fixed perpendicular lines. Coordinate systems are widely used today, including in applications like maps, global positioning systems, tracking weather patterns, and air traffic control, where they are essential for describing an object's location. Without a coordinate system, important functions like air travel would be impossible.