The objective of this paper is to demonstrate that the distortion grid generated by MapAnalyst, a free software package for the cartometric analysis of historical maps, should be computed and interpreted judiciously and not be seen as revealing the immutable structure of implicit parallels and meridians of the map. Awareness of the limitations as well as the capabilities of this software tool is essential. This paper explains the processing method of MapAnalyst and demonstrates in what way this imposes limitations on the analysis of portolan charts. The paper concludes with recommendations on how MapAnalyst can be successfully applied to the analysis of portolan charts and demonstrates this with an example analysis.
