In addition, the charts provided realistic depictions of shores. They were meant for practical use by mariners of the period. Portolans failed to take into account the curvature of the earth; as a result, they were not helpful as navigational tools for crossing the open ocean, being replaced by later Mercator projection charts.[1] Portolans were most useful in close quarters' identification of landmarks.[1] Portolani were also useful for navigation in smaller bodies of water, such as the Mediterranean, Black, or Red Seas.