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E.3. The termini selected for the pelagic statements in the two portolani
There is a need for a full list of the suites of pelagic courses in the two portolani. Patrick Gautier- Dalche’s side-by-side comparison of the statements in the two texts included those from Lo compasso only when they had previously featured in the Liber. Since the later work has many times the number found in the Liber, it seems that there was minimal overlap between the two lists of pelagic termini, which a comparative analysis could test.
E.5d. The discrepancies between the stated pelagic distances in the Liber and Lo compasso
One outstanding question for future research would be to ask when the mileage figures in the portolani started to be repeated by scribes rather than being measured off a chart. Another would test whether subsequent copying introduced corruption in the mileage figures, and, if so, whether those could be used to help trace the lineages of later portolani. To attempt to explain those discrepancies would require the testing of all the examples identified by Patrick Gautier Dalché against true distances.
K.1a. What was the source for the coastal outlines?
As a partial corrective to the generalisation about the broad-brush approach to the continental coastlines, Jacques Mille, who has made a close study of the Provençal shoreline, found recognisable features in the 1313 Vesconte atlas, in particular the Giens Peninsula (The French Mediterranean coasts on portolan charts (self-published, 2016), pp.6-7). However, that is relatively close to the west coast of Italy, where the charts evidently emerged, and that area may prove to have been treated with greater care than elsewhere. An overall examination of the coastline treatment might resolve that question.
K.1b. How were the coasts demarcated?
This aspect deserves further study to see if distinct types of coastline representation can be classified into a typology, and, if so, how realistically that matched with reality. The value for mariners of a visual guide to the shore’s appearance when approaching an unknown coast would be obvious. It is strange that so important a feature seems to have been overlooked by all of us, past and present. However, assuming that the Carte Pisane reflects the style of its immediate antecedents, this possible further innovation must be credited to one of the chartmakers that followed later, perhaps Vesconte, and hence it has no direct bearing on the origin question itself.
It would be a challenging but worthwhile project to extend the systematic Excel toponymic survey to the islands, since that deals only with the mainland names.
K.2c. How were the dangers recorded and how did those get onto the charts?
In relation to the dangers described but left unnamed in the portolani, attempting to match those brief textual mentions with what can be recognised on today’s marine charts could be a valuable project for future research.
A digital tool for comparing text, 'veccompare', has been recently announced and demonstrated – Heather Wacha & Jacob Levernier, 'Cartography and Code: Incorporating Automation in the Exploration of Medieval Mappaemundi', Digital Medievalist, 12(1) (2019) . Could this be applied to the portolan chart toponymy?
The Carte Pisane has around 680 mainland toponyms. Can any of those be reliably ‘dated’, in the sense that the name could not have existed before a known date? If so, the evidence has not yet surfaced. Given the number of modern countries bordering the Mediterranean and Black Sea, and the range of languages involved, how many national, regional, or local historians have examined the Carte Pisane’s toponymy searching for significance of that kind? Perhaps, in the future, more hard evidence will emerge from such investigations.
Further detailed comparative studies of the names on the Carte Pisane and its first successors might well help to clarify the different lineages that might have existed in the period leading up to that first surviving chart.
The portolan charts might have been responsible for another possible effect. By providing the full Mediterranean context, this would surely have increased confidence when setting a course. Many sailors would have been repeatedly following the same routes; could the portolan charts have given them, and their merchant paymasters, the impetus to use new routes?
N.2a. The possible contribution of merchants to the charts’ origin and development
It would be interesting to know if there is any evidence of an increase in the range and length of trading voyages from, say, 1300 onwards. If there was, that might reflect a growing confidence in the reliability of the portolan charts for voyage planning and navigation.
There are no doubt several aspects of the portolan charts’ geometry that could be identified by cartometric specialists as suitable for close examination. The following topics are put up as suggestions.
In order to corroborate (or contradict) what has been suggested in this essay – namely that the overall outlines were derived from a hypothetical diagram of the pelagic termini around the Mediterranean perimeter - the charts’ geometry needs to be submitted to cartometric analysis to see if there is a good match between the positions of features on different sides of the sea. The Carte Pisane and the other very early charts could be tested to see how closely locations on the same north-south line are in fact aligned, and likewise for samples along the west-east, northwest-southeast or northeast-southwest axes. This could be done not only for the Mediterranean but also for the Black Sea. In that case, instead of islands, the projecting Crimean peninsula offered reference points, and the voyages between the separate European outposts must have provided practical navigational corroboration. Comparing those cartographic results with the pelagic statements in the two portolani would be interesting, but perhaps impracticable given the inconsistency in the estimates of distance in those texts.
A.3b.2. Different purposes of al-Idrīsī’s Charta Rogeriana and the portolan charts
So as to understand better the geometric relationship between the Ptolemaic outlines and those on the al-Khwārazmī and al-Idrīsī maps, might a comparative cartometric analysis be carried out? In the case of Ptolemy and al-Khwārazmī, the astronomically-determined coordinates survive. Those could first be contrasted and then perhaps the result compared with the positions of the same named points on the Charta. Would such an analysis confirm or contradict any borrowings, and possibly reveal if such astronomical tables, or even fresh observations, formed part of the Charta’s underlying geometry? [Or has such work already been done?]
E.5b. Why the Liber’s pelagic statements must have been copied from a cartographic document
The modern identifications of the places mentioned in the Liber’s pelagic statements have been provided by Joaquim Alves Gaspar ('The Liber de existencia riveriarum (c.1200) and the Birth of Nautical Cartography'. Imago Mundi, 71:1 (2019): Fig. 7, p.14), but the locations of the termini are naturally taken from an accurate modern map. Plotting out the Liber’s crow’s-flight direction and distance formulae against, first, a modern map and, second, the Carte Pisane, would test the interpretation made here as to the origin and meaning of the Liber’s statements. Would there be sufficient conformity between the plotted positions of the Liber’s termini and the equivalent ones on the Carte Pisane, and likewise between their respective choices of terminal points? If such an exercise was feasible we might then be allowed a partial and indirect glimpse into a very early stage in the chart’s development, and thus come closer to the actual origin than we are likely to do by any other means.
The question as to how the larger islands were placed in relation to the adjacent coastline does not seem to have been tested cartometrically, and there sometimes appear to be minor variations in an island’s overall position in the sea.