Visualization of the Local Distortions on the Oldest Known Urban Map of Seville1771

Resumen

Visual comparison and visual superposition are among the techniques applied in the literature for the analysis of the accuracy of historical maps. Although both approaches have declined over the years and are decreasingly applied in this type of research, they support the conclusions of two previous studies, carried out at the end of the last century, on the accuracy of the first known urban map of the city of Seville (Spain). The map, divided into four sheets, represents, with relative rigor, the image of the city at the end of the 18th century (1771), which has become one of the largest historical centers in Europe. In the wake of its 250th anniversary this research re-evaluates the accuracy of the so-called Map of Olavide, named after the person who led the initiative, by applying a different methodological approach, which analyses each of its four sheets separately. Furthermore, in order to calculate and visualize the local accuracy distortions present in each sheet, the latest tools postulated in the literature for this purpose are used, namely MapAnalyst and differential distortion analysis. The accuracy of the scale bar and the alignment of the compass rose traced on the map are also verified. The results achieved enable the information known pertaining to the accuracy of the oldest urban map of Seville to be improved with new data. Moreover, the careful analysis of the local distortions reveals new findings regarding its topographic survey method, which disputes the main theory hitherto held in this regard.