mountain peak or summit or top
plateau, high plane
deep, hole, depression, hollow
plain, low plane
planes with elevation of their kind under and over water level
having ranges and abysses as borders, depressions and heights as land marks
Assuming a net of measure points all over the globe, we can connect each point with it’s nearest neighbours by arrows, which direct down hill, the direction of the rain fall water flow.
The more points we set, the more accurate our model of peaks, ridges, valleys and hollows will become.
maximum: all arrows direct away
minimum: all arrows meet
saddle point: two opposite arrows meet and the orthogonal arrows direct away, a valley crossing a ridge?