A nautical chart has a very detailed and accurate map of the coast line, also taken into account with these maps are variations in tidal levels and water forms, this can be critical to anyone who is trying to navigate.
Also a chart is a working document, it is used to plot out the courses for ships. These charts show a unique set of characteristics which helps navigation, some of them characteristics are a draft, bottom clearance, wrecks and obstructions which can lead to an accident if not correctly navigated away from. The map also has landmarks on it, this can be good if you get lost they can then be used as a reference and can also be used if a change of course is needed.
Another thing it shows you is the surface area beneath the sea, this cannot be seen by the human eye, and prevents many accidents.
A map is only used basically for land, a map cannot be used to plot a course for a ship as the only image of the sea is at sea level. A map gives a pre plotted course, for example, a road, something which is normally followed. Also a map doesn’t count for what type of vehicle you are in, if you look for the quickest route but you are in a lorry and you have to navigate tight bending roads then that would be a problem.
Maps offer no reference to what the ground below is like, if a road had road works on it, you wouldn’t know because a map is a static document. It leaves it up to you to go to that road then make a visual assessment, normally by that time it is too late and you are forced to go navigate around it or turn back. New maps do have some of this information but very rarely as the state of a road can change rapidly.