El puerto de El Callao, en el mar Pacyfyco, o de el sur. Con las costas ymmediatas a el de Barlovento y Sotavento, Yslas y arrecifes que se comprehenden y la sonda numerada en Brazas. Levantado de orden del rey nuestro señor año de 1744.

Map of the port of Callao, Peru, and the bay. The cartographic elements include the compass rose, topographical details and the scale. In the lower right corner is the key in which the places (ports, beaches, towns, etc.) identified by letters on the map are listed. The letter H indicates the location of the City of Lima, capital of Peru. Callao was and still is the largest port in Peru. It was founded in 1537 and was the principal port for Spanish trade in the Pacific, handling the exports of Peru, Bolivia and Argentina. In 1746, a tsunami caused by an earthquake destroyed it. Towards 1732 there were still disagreements regarding the shape of the planet, which is why the Academy of Sciences of France, with funding from King Louis XV, undertook two expeditions (one in the Arctic and another in the equatorial zone in the Viceroyalty of Peru) whose aim consisted of measuring the length of one degree of terrestrial meridian to settle the aforementioned controversy. Thus, in 1735 the French Geodesic Mission was established to verify the measurement and shape of the Earth, a scientific expedition directed by Pierre Bouguer and which in Ecuador had the participation of two outstanding figures of the Spanish scientific Enlightenment: the sailors Antonio de Ulloa and Jorge Juan de Santacilia. In Guayaquil, they established the base of their observations consisting of geodesic triangulation, a procedure that was not easy owing to the climatic and physical conditions of this equatorial region. To these difficulties were added the disputes between the French academics who accompanied this expedition, as well as the mistrust they aroused among the indigenous population and the local authorities. For these reasons, the measurement tasks ended up covering a period comprised between the years 1736 and 1744. In 1740, Juan and Ulloa had to interrupt their scientific observations because the viceroy summoned them to service to defend the Pacific coasts, principally Guayaquil and El Callao, against the attacks of the English commodore George Anson. Both sailors patrolled the coasts of Chile, a circumstance they took advantage of to make measurements and observations, and to draw up plans of the coasts, bays and cities through which they passed. Back in Spain in 1748, the two sailors jointly published the Relación histórica del viaje a la América Meridional, a work in four volumes written by Ulloa that covered information on the history, politics, geography and ethnography of the viceroyalty; as well as the Observaciones Astronómicas y Phisicas hechas en los Reinos del Perú, written by Jorge Juan, where the scientific results of the measurement of the Earth are gathered. These results, compared with those obtained by the French expedition in the Arctic, confirmed that the Earth is a geoid flattened at the polar zones.