It is not clear when this map was drawn but given the appearance of the Citadel it must be after 1660. By this time, Plymouth had withstood a four year long siege during the English Civil War. It is interesting that the Stuart built castle seems more imposing on the people of Plymouth than on any potential would be invaders from the seaward side!
Stonehouse is shown as a tiny settlement off to the west. Millbay marshes seem to extend quite far and help in isolating the two settlements from one another.
Empire in Your Backyard: Plymouth Article