Benincasa
He, and evidently some other chartmakers, seem to have worked at specific different scales. If this is confirmed, can the characteristics of two, or even three, different workshop models be identified? [On which see Benincasa: Models].

A systematic general study of his productions could be made, focusing particularly on toponymy, based on an archive of scans for the period after 1469 (which is covered on the Pujades 2007 DVD).

Carte Pisane
See the separate page of future research possiblities arising out the extended essay on the dating of the Carte Pisane (2015)

Colour
The C&SA methods could be extended to other islands and features, for example the Adriatic islands.

A paper was delivered at the Library of Congress portolan chart conference on 21 May 2010 by Fenella France, 'Scientific and Image Analysis of Portolan Charts: Preliminary Results and Methods'. This referred to 'assessments of things like colorants that indicate whether these charts may or may not be commensurate with the suggested timeframe', and might 'allow a source or location for the inks and colorants to be suggested'.
    Though difficulties would always remain, my very approximate colour judgements could be improved and a more precise idea gained as to the consistency of their use.

Copying methods
(On which see Stages in the construction of a chart)

The outstanding questions seem to be these. Many of them could be best answered by practical experimentation, or by high resolution portolan chart scans if those could be compared, either side-by-side on a computer screen or via enlarged downloaded details:

1. How was the information conveyed from one table-sized chart to another?
2. Was a special desk needed? Might there have been customised tables with slots in so that the relevant portion of the model could be brought close to the copyist, particularly when entering the names? Or for charts, which would always be rolled inwards, might this have allowed work to continue on a succession of vertical bands? The techniques used for copying books would hardly have been adequate and the 1318 Vesconte illustration ('Chapter' plate 31) probably shows an atlas sheet. Alternatively, would the vellum have had to be kept tightly stretched so as to present a perfectly flat surface, e.g. for drawing the rhumb lines?
3. How were models at different scales produced (assuming that the practitioners could not, or did not, directly copy at a different scale)? Are there distinct models at two or more different scales? If so, how consistent is the placement of headlands on the different versions?
4. Exactly how were the coastal outlines transferred from the model to new work in the 14th century and what traces can be seen of that (or those) process(es)?
5. If pouncing was used, presumably transferring only significant points along the coastline, that would mean the intervening sections were added freehand. This has been found to be the case with some chartmakers. Will close comparison of a wide range of charts confirm that that was the general rule, at least before the 16th century?
6. What did or did not form part of the coastline model, e.g. which of the islands were traced and which drawn freehand? And was that distinction the same for all chartmakers?
7. If it proved possible to identify the unique characteristics (or 'signature') of a single pattern (perhaps indirectly via cartometric comparison of the placement of a chart's nodal points, usually headlands) could successive patterns used by a particular chartmaker be distinguished, and patterns taken over or copied by one chartmaker from another be identified?
8. The 15th-century Benedetto Cotrugli described placing a ruler across a chart, between three specified pairs of places. If no islands intervened the chart was 'right'; otherwise it was wrong (Falchetta, 2008, p.271). Might this be a way to distinguish different patterns, or even different 'schools'?
9. Could a cartometric analysis, focusing perhaps on enlarged sections, resolve the points above?
10. Is it possible to confirm the existence of separate, probably sectioned, toponymic models?
11. If two or more people were working on a chart (sharing the writing, or dividing writing and painting) could they have worked simultaneously (to speed production) and, if so, how did they physically manage (see [2] above)?
12. Is it possible to distinguish between the work of someone who had served a chartmaking apprenticeship and somebody who was just given a chart to copy, and can those differences be codified?

Michael J. Ferrar's online essay of November 2013 (pages 12-14), Leather, Vellum, Parchment; Drawing and copying maps and charts provides his suggested answers to the questions above.

A number of the questions above have been answered in an article that is the necessary starting point for consideration of these issues, namely the detailed and systematic investigation of the methods definitely or possibly used in portolan-chart copying see Šima Krtalić, ‘Anchoring the Image of the Sea: Copying Coastlines on Manuscript Nautical Charts from the Late Middle Ages and the Early Modern Period’, Imago Mundi, 74:1 (2022): 1-30. {This paragraph added 13 July 2022}.

Dating and attribution
Nearly half (roughly 50 out of 110) of the charts and atlases thought to have been definitely or possibly created in the last half of the 15th century lack any certain dating – whether the year in question was explicit, estimated or loosely assigned – and few have even a suggested attribution. Perhaps it would already be possible for existing technology – and if not now surely quite soon – to be brought to bear on the uncertain dating and authorship of such a sizeable cohort.

Even if a digital palaeographic comparison did no more than determine if any two or more works were in the same hand it would be a useful first step. Alternatively, the form of the place-names might sometimes throw up further, or corroborative, pairings. It seems likely that most of these little-studied charts will be Italian, and some might be examples from a putative official Venetian workshop. If so, many different hands could have been involved, but the toponymic forms would surely have been broadly consistent. Since no toponymic innovations related to a dateable event have yet been identified for the later 15th century, or indeed the early decades of the 16th century (see ”Toponymic time-lag (from physical creation to recognition by mariners”) it is possible that some charts will, with further research, need to be moved from one century to another.

Even though confirmed datable names may have not been recognised, another approach might be tried. The Excel listing notes the first time a toponym had been recorded on a dated chart. 80 of those innovations have ben noted between 1450 and 1500 and a further 60 up to 1550. Sorting the spreadsheet on Column F and A would both isolate those added names in chronological order, and provide some geographical refinement. Any findings would likely be no more than indicative of a date but they might point to a particular chartmaker or model. {This paragraph added 23 June 2023.} One particular event does, however, mark a dividing point, namely the arrival of the Knights in Malta in 1530, closely followed by the addition of their cross to that island on portolan charts. (This sentence added 9 July 2023.}

One aspect seems not to have been considered, namely what can be learnt from the content of portolan charts of the Mediterranean that appear in atlases, since these (even if lacking a specific year) can usually be datable in terms of the 16th-century discoveries visible on other sheets.

Such an exercise is now feasible because of the ”MEDEA Chart Database“, which specifically incorporated images of as many as possible of the works listed in my ”Census”. This reciprocates by including a separate MEDEA column. {This section added 19 June 2023}

Flags
With the use of extracted details, a complete vexillological catalogue could be produced of the flags on early charts. Matched against known historical developments, this would refine our understanding of the level of chartmakers' responsiveness to change, both individually and collectively.

Handwriting
If it was possible to obtain enlarged samples, preferably from every production, a visual catalogue of much-enlarged details of distinctive letter forms could be created. Ideally, it should be possible to compare several of those details directly on the screen. This might make it possible to determine (a) if further anonymous works could be assigned to a named chartmaker or shown to exhibit shared authorship, (b) how many charts are in more than one hand, (c) how many signed charts are actually in the hand of a collaborator, and (d) if the signature was always in the hand of the chartmaker himself.

Navigation hazards
An interesting comparison could be made between the early portolani and the portolan charts in relation to offshore navigation hazards. A number of the place-names are identified in the texts as rocks, sands or shallows. Where those can be identified today, a check could be made to see whether the charts depicted them, and if so how realistically. The shape and placement of the red and black symbols for navigational dangers might be compared on different charts, e.g. are all present on the functional ones? A separate exercise might compare those with a modern chart to see how accurate they were. [Update: All the above points were investigated during 2015-16 and await publication.]

Ornamentation
The illustrative details on ornate charts might be closely compared to see if they were sometimes copied, or even traced, from one another - both within the production of one chartmaker and elsewhere. Could an art historian distinguish the work of different individuals, even if they could not be named?

Why did Roselli introduce decorative elements at a certain stage and then discard some of them later? What is the explanation for Ziroldi's distinctive 'middle' period? [On which see Attributions: Roselli and Attributions: Ziroldi.]

Physical analysis
Increasingly sophisticated techniques of scientific investigation - inevitably requiring access to originals and so probably involving only a few charts - could perhaps answer some of the colour questions, if only for those works examined. Perhaps it could be determined if what now appears black might originally have been silver. Likewise they could establish conclusively, even if just in the few sampled cases, the precise order of construction. If that proved to vary between chartmakers, it might turn out to have diagnostic value as a 'constructional signature' and one that could help to identify the work of copyists.

Practitioners & Workshops
In an attempt to understand better how chartmakers and their collaborators might have operated, parallels could be sought from related professions - without losing sight of the several unique aspects of portolan chartmaking.

Venetian practitioners. The systematic work of dating and attribution done by Pujades has drawn attention to the large volume of charts emerging from Venice (particularly in the 15th century and about half of it unsigned). Overlapping similarities among some of the anonymous productions, but in different hands, suggest that different working arrangements might have operated there, perhaps some kind of 'co-operatives'. Can more information be found in the Venetian archives?

It seems that the use of red for a particular name, and sometimes even its presence at all, forms part of that practitioner's unique 'signature'. Perhaps that could be tested to see if it helps in attributing unsigned or incomplete works. [On which see Rare and unique names.]

Occasionally a name would be written inland, with a line of dots running to its correct coastal position. It seems that that might be a technique used only by Venetian practitioners of the early 15th century. [On which see Drafting conventions.]

The portolani and open-sea voyages
A cartometric exercise might be carried out to test the accuracy of the distances given for the pelagi, or open-sea voyages, described in two 13th-century texts, the 'Liber de existencia riveriarum' and 'Lo compasso de navegare' (see Gautier Dalché, 1995, pp.205-19, 304-5, and Debanne, 2011).

Shape
A cartometric exercise could determine the accuracy of the initial positioning of the salient capes found on the larger islands, both in relation to the continental coastlines and also to one another. Tests over time could demonstrate if there was later improvement or degradation.

A better understanding could be obtained of the development, or otherwise, of the shapes of smaller islands, particularly those not included in the C&SA.

16th & 17th centuries
Several of the points examined for the period before 1500 were continued, via sampling, into the later period. Systematic studies for the 16th, and even 17th century, would complete, and no doubt amend, my findings.

Toponymy
Ideally, the full transcription would be made of all the names on all the accessible charts, up to an agreed date and selectively thereafter.

The expanded and revised general listing of mainland place-names, added in September 2013 as an Excel spreadsheet, includes the equivalent toponyms from the 'Liber de existencia riveriarum' and 'Lo compasso de navegare'. This would enable a systematic comparison between the early portolani and the portolan charts, in terms of both incidence and name forms. [This would replace the preliminary findings set out in Later introduction of 'precursor names' seen on selected early works (a Microsoft Word document).] {Update: such an investigation was carried out for the Carte Pisane investigation (March 2015)}

Is there a tendency for the toponyms of headlands to be positioned with some accuracy, in relation to the relevant feature, whereas the intervening names were evenly spread out?

The source used for the 1595 Barentsz sea atlas of the Mediterranean could be identified and the relationship established between the other early printed pilot books and their manuscript predecessors.

One possible line of enquiry would be to list the direct, long-distance sailing routes (the pelagi, or variant spellings of that) in the surviving portolani - see Gautier Dalché (1995, pp.304-5) for relevant maps from the 'Liber de existencia riveriarum'. If the destinations change over time it could be revealing, particularly for an understanding of toponymic development and trading history.

An examination could be made of the toponymy on charts produced outside the Mediterranean, e.g. those constructed in Lisbon, Dieppe or London during the 16th and 17th centuries. A superficial examination indicates that there are interesting differences, for example in the English names for the north-west French coast.

Toponymy (Religious references)
Churches and saints' names:
Some saints' names recur regularly, for example George [zorzi, etc]. A number of instances of s. /san/ sancto nicolo/nicola were also noted. Might these in some cases refer to the towers or spires of churches or other religious buildings that provided sailors with landmarks? Certainly ten such churches are listed in 'Lo compasso de navegare' (see the 'Indice toponomastico' in Debanne, 2011). Or could they refer to the naming preferences of an individual chartmaker or refer to his city's patron saint?

'sante parole':
Besides physical locations with saintly associations, the medieval sailor recognised a virtual sacred geography that assigned a prominent or local saint for each section of the coast. These became sante parole, in the text surviving in Florence, described by Michele Bacci in 2003, but la bonna parolla in a second extant (Ligurian) manuscript in Genoa, recently announced by Valentina Ruzzin (2013). Each version has around the same number of names (130) but the latter, which dates no later than 1351, doubles the total around Genoa. The geographical spread is similar – around the northern and eastern shores of the Mediterranean and, selectively, as far as Flanders and the British Isles.

The main difference between the two versions is that the Florentine manuscript specifies that the prayer assigned to the saint associated with that part of the coast must be said at a time of danger, while the Genoese version is intended to be recited before sailing from the home port. Each of the authors lists the names and locates those on a map.

How many of those names can be matched to portolan chart toponymy? It seems reasonable to conjecture (and perhaps documentary proof may exist) that the toponymic catalogue in the portolan chart could have played a useful role in providing the relevant place-name when a threat materialised.

I owe these references to Ramon Pujades and Corradino Astengo, respectively. {This 'sante parole' section amended and extended 1 July 2016}

See also a collection of papers delivered at the Fribourg Colloquium in 2013 - under Michele Bacci & Martin Rohde (2014) in the general Bibliography; and also Bellomo (2008). {This sentence added 2 February 2018}

A possibly related religious application was suggested by Laura De Marchi (2015), in connection with Vesconte's atlases. She states that "Vesconte’s atlases are the result of collaboration between Pietro and a workshop of Venetian illuminators ... The article explains why numerous figures of saints can be found in these atlases and suggests a possible practical use, as manuals for consulting places during a sea voyage and for prayer". {This paragraph added 24 July 2017}