Four centuries of cartographic depiction of the island of Puerto Rico from old maps

The cartographic depiction of the island of Puerto Rico from 1493 to 1914 is examined using 52 public old maps. Analysis reveals that the depiction of the island’s shape evolved from rectangular, to mixed rectangle-trapezoid, to trapezoidal. The island’s centroid was positioned near its accepted value of 18.25°N soon after its discovery. Old maps allowed estimating the width of the island as 0.7°, close to the modern value of 0.56°. Georeferencing allowed estimating the area and perimeter of the old maps using a 6-point affine (6PAT) and similarity (ST) transformations to compared the results. Both time series of the area (A) and perimeter (P) exhibit temporal oscillations. The area was similar under both transformations, but the perimeter from the ST was larger than that from the 6PAT. Map scale and island shape help account for the changes in the area and perimeter from the 6PAT, but not from the ST. Results showed that from 1500 to 1820, the island depiction was rectangular, from 1820 to 1900, the depiction became trapezoidal. These improvements reflect advances in astronomical navigation, navigators’ knowledge and skills, the introduction of the sextant, chronometer, Greenwich Meridian, and modern cartographic projections. We offer some suggestions for the georeferencing of old maps.