Early hydrographic surveys consisted of depths calculated by sounding pole and hand direct line, with positions determined by 3-point sextant fixes to mapped reference factors. Guide strains have been ropes, or traces, with depth markings and lead weights hooked up. When analyzed, The situation may be marked on Exclusive charts. https://sethapkyw.eedblog.com/32271094/new-step-by-step-map-for-hydrographic-survey-in-bangladesh