Naslov
Reflection of the Perception of Spherical Coordinates for the Adriatic Sea Area on the Accuracy of Early Modern Nautical Charts and Geographical Maps

Autori
Marelić, Tome ; Faričić, Josip

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, neobjavljeni rad, znanstveni

Skup
17th International Conference on Geoinformation and Cartography

Mjesto i datum
Zagreb, Hrvatska, 23.09.2021. - 25.09.2021

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Domaća recenzija

Ključne riječi
early modern nautical charts ; early modern geographical maps ; spherical coordinates ; Adriatic Sea

Sažetak
During the last three centuries of the Middle Ages, portolan charts were made in the Mediterranean. Their mathematical basis can be directly determined from linear scale bars and, conditionally, from the rhumb network, as in the first centuries of their production the graticule grid was not plotted on them. The display of a graticule grid, the appearance of which depends on the applied map projection, is a legacy of Hellenistic cartography. However, the awareness of the possibility of making maps in such a way that their mathematical basis rests on the spherical coordinates of points on the Earth projected into the plane, reached Western Europe at the beginning of the Modern Age, primarily through Claudius Ptolemy's Geographic Hyphegesis: the fundamental work about the spatial interrelations perceived in this manner. Since the early modern period, the display of the graticule network became a standard in the production of geographical maps, and, later, nautical charts. This research sought to determine the accuracy of the representation of the Adriatic Sea on early modern nautical charts and geographical maps, taking into account the values of the spherical coordinates displayed therein. On the selected charts and maps, a sample of points standardized among them was determined, for which the average error of spherical coordinates in relation to their actual values was calculated. In addition, the average error of the spherical coordinates was calculated for the selected geographical maps in comparison with coordinates extracted from the Geographike Hyphegesis. Nautical charts and maps were then georeferenced over a modern map projected in three selected map projections in two different scenarios: a) by using the selected points’ actual coordinates as reference values and b) by using the points’ coordinates extracted directly from maps and charts themselves as reference values. Our results showed that the coordinates on the selected maps are more accurate in comparison with their actual values than in comparison with the values extracted from Ptolemy's work, whose influence on the production of these maps is manifested in their relatively high longitudinal errors. On the other hand, the range of longitude and latitude degrees on nautical charts shows more significant deviations from analogous values found on maps, and according to the spatial composition of the selected points they appear to be geometrically more similar to portolan charts. On the basis of this, it was assumed that the longitudinal values on charts containing a graticule grid, in comparison with selected maps, were additionally corrected in such a way that their authors had plotted the graticule over the spatial display typical for the portolan charts, which had, by then, already been in use. According to the point coordinates values that were extracted directly from the maps and charts sample, it was found that selected maps were mainly projected in a normal equidistant cylindrical projection with latitude 36° used as a standard parallel, while selected charts were, for the most part, projected in normal conformal cylindrical (Mercartor) projection. Considerably high geometric accuracy for both maps and nautical charts was determined, in terms of their particular cartographic projections, when the values of spherical coordinates are taken into account in the way they were perceived by their authors. Our research results also indicate that compilation was one of the basic methods of the composition of geographical content on these maps and charts and that, for the most part, the geographical and nautical cartography of that period behaved as two parallel and relatively separated systems in the context of the perception of spatial interrelationships, with geographical cartography relying on the preserved opus of Claudius Ptolemy, and nautical cartography on the geometry of portolan charts coastline renderings.

Izvorni jezik
Engleski

Znanstvena područja
Geodezija, Povijest, Geografija

POVEZANOST RADA