This research analyzes the earliest located floor plan of the Mosque-Cathedral of Córdoba, an anonymous oil painting in 1741, which has not been studied so far. The objective is to know the dimensional accuracy of the most relevant architectural forms drawn, considering the elements referenced in their legend and the graphic symbols used, to assess their documentary interest. It has also been compared with two important plans of the Mosque-Cathedral drawn in 1767 and 1868. The first task was a photogrammetric survey of the oil painting has been carried out. Subsequently, some data has been measured in the monument using a 3D scanner. The orthophoto of the oil painting has been overlapped to the digital model to verify its metric accuracy in a selection of points. For the first time, the legend and labels included in the oil painting have been transcribed. This precise graphic document contains reliable abundant data for future research about the transformations and restorations of a monument that is part of the UNESCO World Heritage List. The oil painting dating from 1741 can be considered as the first scientific plan of the Mosque-Cathedral of Córdoba, and as an outstanding architectural survey of eighteenth-century Europe.