It is possible to know what something looks like without seeing it. Most models of the ocean floor are vertically exagerated. Topographic maps can show a three dimensional surface on a flat sheet of paper. Land forms on the sea floor are similar to land forms on the continents.
Many factors affect the accuracy of scientific investigations.
Background Oceanographers have discovered the shape of the ocean floor by measuring the depth of the ocean in many places. Early tools included lead weights, lowered on marked ropes or cables to the ocean floor. From such depth readings, scientists gradually built a picture of the ocean floor they could not see. These methods were very slow and eventually were replaced by sonar systems which bounced sound waves off the bottom. Today, sophisticated side-scan sonar and satellite data are fed into computers that are giving us the most detailed pictures of the ocean floor ever obtained.