means A person trained to measure and map land, boundaries, buildings, or terrain with precise instruments, defining where one piece of ground ends and another begins.

from From the Anglo-French surveeir and Old French surveoir, 'to look over, oversee,' built from Latin super- ('over') plus videre ('to see') — a cousin of words like 'vision' and 'video.' So at root a surveyor is simply someone who looks down over things; the leap to measuring land came later, as overseeing turned into the careful business of marking exactly what was being looked over.