Cuba, Hispaniola, and Puerto Rico, the focus of Spanish colonial interest in the West Indies, are depicted on this 1799 nautical chart of the Greater Antilles, published by the Spanish Hydrographic Office. It is based on information provided by Spanish admiral Juan de Langara, who participated in several battles for possession of the islands. At the top, there are seven headland views, provided to assist sailors in easily recognizing island and harbor coast lines. The legend also notes how latitude and longitude were computed for various sites. During this period, computation of longitude had not been perfected, and the east-west position of a ship was calculated using a variety of methods including astronomical observations (comparison of the time on ship of a predictable astronomical event with the time it would have been visible at a prime meridian) and maritime clocks (the use of two clocks, one set to local time each day at noon, and one set to the time at a prime meridian). In this case the prime meridian, the point from which longitude was measured, was Cadiz.