Why did marking the high elevation points determine the watershed's edge?

Marking the high elevation points is crucial for determining a watershed's edge because these points, known as ridgelines or divides, define the boundaries of where water flows. Water naturally flows downhill from higher elevations to lower ones, so the area where all precipitation collects and drains into a single body of water is delineated by these high points. By identifying them, hydrologists can accurately map the watershed and understand its hydrological dynamics. This delineation is essential for effective water resource management and environmental conservation.