Determination of definitive standard parallels of normal aspect conic projections equidistant along meridians on an old map

Abstract

ABSTRACTIn previous research we proved that meridians are straight lines and parallels are arcs of concentric circles on the map Nuova carta geografica dello Stato Ecclesiastico by J. R. Bošković and Ch. Maire, published in 1755. We also proved that the map was produced in a normal aspect conic projection equidistant along meridians. Knowing the map projection type is not enough. We need to know its parameters, too. In the first part of the paper, we described the procedure of determining standard parallels of the normal aspect conic projection equidistant along meridians. We proposed a procedure for determining projection parameters of an old map, especially its standard parallels, if the radius of the sphere in which the map was produced in is unknown. Constant C is introduced as a ratio of constant K and sphere radius R, both of which are unknown. The procedure is illustrated on the map Nuova carta … . Using the procedure, we obtained standard parallels φ1 = 41°50'N and φ2 = 44°30'N. In addition, we tested whether the obtained standard parallels are actually standard parallels in which the map was produced and determined the definitive standard parallels in which the map Nuova carta … has been produced.