The work offers a systematic geographical and historical survey of Portugal, pairing detailed local descriptions and river, town, and provincial notices with political and secular history. It explains mapmaking principles—latitude and longitude, meridians, tropics, poles, and the use of lunar eclipses to estimate longitudes—and discusses variations among cartographers' coordinates. The author aims to correct foreign misconceptions by providing precise measurements, comparative tables of coordinates, and annotated maps. The text combines practical instructions for reading maps with regional topography and place-by-place entries intended for both native and foreign readers.