What is main advantage by using a Mercator map?

Answer 1

When the Portuguese, under the leadership of Prince Henry the Navigator, ventured farther south along the west coast of Africa, they encountered navigational difficulties by assuming that the charts used in the Mediterranean could simply be extended. Over long distances the rhumb lines could not be taken as straight, and the charts bore no relation to the new methods of checking the dead reckoning that Portuguese astronomers and mathematicians had devised. These methods required a chart on which positions were expressed as latitudes and longitudes rather than bearings and distances. Such a chart had to embody a practical method of representing the curved meridians and parallels on a flat surface. Even for an area as large as the Mediterranean, this can be done without grossly falsifying either distances or directions, but for larger regions some distortions are inevitable, and a choice has to be made between alternative mapping techniques. On certain types of charts, distances can be shown accurately, but directions cannot; on other types, directions are reliably presented, but the scale of distance varies greatly between different parts of the chart. The navigator accepts the second type because the risk of lengthening the voyage is preferable to that of missing the target.

Answer 2

they provide sufficient boundary lines and conatin great structured mountains!