Early hydrographic surveys consisted of depths calculated by sounding pole and hand lead line, with positions determined by a few-level sextant fixes to mapped reference factors. Guide lines were being ropes, or lines, with depth markings and guide weights attached. These charts involve historic features, which include LORAN-C traces. Hydrographic https://trentonhnsvy.jts-blog.com/31433078/new-step-by-step-map-for-hydrographic-survey