Roel Nicolai

The origin of nautical or portolan charts poses the greatest challenge of the history of cartography. Claims that the ‘big’ questions have been answered and research can therefore focus on filling in the details are unfounded. Majority opinion still holds that portolan charts are medieval creations. Although there is a complete absence of historical evidence that supports a medieval origin, evidence that contradicts such an origin does exist. In the absence of historical records, quantitative (cartometric) analysis is a relatively novel technique that can reveal new facts about these charts. Cartometric analysis has shown that portolan charts are composites of accurate regional charts. These regional charts agree surprisingly well with a modern map on the Mercator projection. Both their correspondence with this projection and their accuracy are incompatible with a medieval origin. This has revealed a conundrum that is still able to raise the temperature of any debate on this fascinating subject.

This is an Open Access article .

Geodetic referencing of seismic navigation data is required for the correct interpretation of the coordinates. To assist in providing the right definition of the Coordinate Reference System of the data the EPSG Geodetic Parameter Dataset has been published since 1994. This dataset is the largest collection of geodetic parameters available globally. As such it has become the de-facto standard for geodetic referencing of spatial data in many communities. It is recommended by SEG for obtaining the relevant geodetic definitions. Previously only available as a MS-Access file, it is now accessible over the World Wide Web using standard Internet browser software. Users can now query the server-based dataset through the EPSG Geodetic Parameter Registry through an intuitive interface, as well as obtain the MS-Access database file. The EPSG Registry also permits software-to-software querying and retrieving of geodetic parameters. This permits new generation software to extract these parameters from the Registry at run time or as part of a periodic synchronization event. The Geodetic Parameter Registry was constructed under a Joint Industry Project facilitated by the International Association of Oil and Gas Producers (OGP).

The rapid uptake of GPS in the offshore positioning industry of the early 1990s led to quality control becoming a topical, but controversial issue. The providers of GPS positioning services used their own, usually arbitrary, ways of defining positioning quality and monitoring the performance of their services, which created significant problems in the management of positioning contracts. Driven and written by Shell (Nicolai), the UK Offshore Operators Association (UKOOA) published a set of standardised quality measures in 1992, which this paper describes and elaborates. It was later in 1994 superseded by the publication of full UKOOA guidelines, which, in turn are now superseded by the “Guidelines for GNSS positioning in the oil and gas industry”, published in 2011 as report OGP 373-19. The principles described in the paper are still valid.

In the 1970s and 1980s hyperbolic positioning systems still dominated the offshore environment, because of their capability of admitting an unlimited number of users. While two ‘patterns’, generated by three shore-based transmitting stations, were in principle enough for determining the ship’s position, a fourth and sometimes a fifth and sixth shore station were added, initially to extend the coverage area of the positioning system, but this could rarely be done without creating overlap areas, in which commonly three useable patterns were available. The third pattern also created the possibility of checking the ship’s position. Cycle slips (‘lane slips’) in the pattern measurements the bane of hyperbolic positioning systems at the time and the detection of the occurrence of a lane slip was seen as a principal objective of the checking capability. But, when an inconsistency was revealed, it would still be still unclear which the affected pattern was. This paper takes the detection of lane slips a step further and describes an innovative method to discover the faulty pattern by means of statistical testing.

In this 1990 paper, presented at the XIXth International Congress of the International Federation of Surveyors in Helsinki, the principles of Least Squares Adjustment and quality measurement and control are placed in the context of the Quality Management Policy, applied to offshore surveying projects related to seismic acquisition and engineering surveys (the installation of offshore oil- and gas production facilities). Although the surface positioning systems used in 1990 have been replaced now by GNSS, the approach to survey quality is still valid.

In the 1980s computing power increased sufficiently to allow more rigorous techniques for processing and quality control/assessment to be introduced in position determination in the offshore industry. This paper is one of the pioneering efforts to introduce such techniques. The paper was presented at Hydro 88 Conference in Amsterdam, organised by the Hydrographic Society and was published in its proceedings.
The paper introduces concepts and methods from what is known as the “Delft School of Geodesy” to the offshore industry. Although nearly 33 years ago now, these principles are still valid and are actively used.

In the second half of the 20th century, a number of developments took place at the Faculty of Geodesy of Delft University of Technology that drew much attention, nationally, but definitely also internationally. These developments were very influential in geodetic, land and offshore surveying practice and currently have a significant impact on GNSS positioning processing and quality control. These concerned the way in which reconnaissance surveys were conducted, measurement results processed and particularly the manner in which measurement quality was assessed. In the world of geodesy these developments are collectively referred to as the Delft School. Its most important pioneers were Jacob Menno Tienstra, his successor Willem Baarda and their co-workers. Their active contributions to this field span the period from 1930 to 1980 and that is roughly the period that is described in this monograph.
This monograph was written by Martien Molenaar, a geodesist who wrote his PhD thesis on research in the context of the Delft School in Geodesy. He was a professor of Geo-information Science and Earth Observation at Wageningen University. In the last phase of his career he was President of the International Institute for Geo-information Science and Earth Observation (ITC), which is now a faculty of Twente University in the Netherlands. The translation was prepared by Roel Nicolai.

The shape of Africa on Iberian nautical charts of the late-fifteenth and early-sixteenth century is surprisingly mature. The portrayal of the outline of Africa on the Cantino planisphere of 1502 is so good that it was not surpassed in the next two, possibly three centuries. The African coastline on the Cantino planisphere is a mosaic of accurate regional charts on the plate-carrée projection, each with its own scale and orientation. The same holds for its Iberian predecessors. The shape of the parts of Africa depicted on these regional charts was essentially correct on the oldest chart (c. 1471) and was copied to later charts. The projective properties of the regional charts are incompatible with the navigation and charting techniques used in that period. Therefore, serious doubt is cast on the established view that Portuguese pilots and cartographers were the original creators of the source charts.

The sudden appearance of portolan charts, realistic nautical charts of the Mediterranean and Black Sea, at the end of the thirteenth century is one of the most significant events in the history of cartography. By using geodetic and statistical analysis techniques, these charts are shown to be mosaics of regional charts that are considerably more accurate than has been assumed. Their accuracy exceeds medieval mapping capabilities. These regional charts show a remarkably good agreement with the Mercator map projection. It is demonstrated that it is very unlikely that this map projection is an unintentional by-product of the charts' putative medieval construction, as is widely believed. While the physical charts are without doubt medieval, the possibility is eliminated that the charts are original products of a medieval Mediterranean nautical culture, which until now they have been widely believed to be. Their true origin must lie considerably further back in time.

The sudden appearance of portolan charts, realistic nautical charts of the Mediterranean and Black Sea, in the last quarter of the thirteenth century, is considered to be one of the most significant events in the history of cartography. Using analysis techniques available in geodesy, Nicolai showed that these charts are mosaics of regional charts that are considerably more accurate than had been assumed earlier. The good agreement of these regional charts with the Mercator map projection is even more remarkable.
Map projections were unknown in the Middle Ages and the Mercator projection was developed some three centuries after the appearance of the oldest extant portolan chart.
Therefore, virtually unanimous agreement exists among historians of cartography that its map projection must be coincidental. Using probability calculus, the author shows that it is very unlikely that the map projection emerged as an unintentional by-product of the charts’ construction.

This paper demonstrates 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.

In the run-up to the Second International Workshop on the Origin and Evolution of Portolan Charts, Lisbon, June 7-8, 2018 I wish to share an article that was published in Issue  52 of the journal "Maps in History" of the Brussels Map Circle (www.bimcc.org).

Portolan charts are highly realistic medieval charts that show remarkably accurate coastlines of the Mediterranean and the Black Sea. They emerged suddenly, without any predecessors or a clear developmental path, in Italy during the thirteenth century. There is broad scholarly agreement that these charts are original creations of European medieval culture. However, corroborating evidence is lacking, and a convincing explanation of the method of their construction has so far not been provided. In this essay it is demonstrated by means of geodetic analysis that the overall shape of the coastlines corresponds closely to that on a modern map based on the Mercator projection. It is further demonstrated that this correspondence cannot possibly be due to chance. Consequently, the existence of a Mercator or Mercator-like map projection on portolan  charts is incompatible with the assumed medieval origin of these charts. Portolan charts are far more sophisticated than has hitherto been recognized. Their construction was well beyond the capabilities of cartographers from either medieval
Europe or the Arabic-Islamic world. This conclusion serves to reopen the question of the origins of the geometric data and the construction methods that until now haveappeared to underlie medieval portolan charts.

Portolan charts are highly realistic medieval charts that show remarkably
accurate coastlines of the Mediterranean and the Black Sea. They emerged suddenly,
without any predecessors or a clear developmental path, in Italy during the thirteenth
century. There is broad scholarly agreement that these charts are original creations of
European medieval culture. However, corroborating evidence is lacking, and a convincing
explanation of the method of their construction has so far not been provided.
In this essay it is demonstrated by means of geodetic analysis that the overall shape of
the coastlines corresponds closely to that on a modern map based on the Mercator
projection. It is further demonstrated that this correspondence cannot possibly be due
to chance. Consequently, the existence of a Mercator or Mercator-like map projection
on portolan charts is incompatible with the assumed medieval origin of these charts.
Portolan charts are far more sophisticated than has hitherto been recognized. Their
construction was well beyond the capabilities of cartographers from either medieval
Europe or the Arabic-Islamic world. This conclusion serves to reopen the question of
the origins of the geometric data and the construction methods that until now have
appeared to underlie medieval portolan charts.

The sudden appearance of portolan charts, realistic nautical charts of the Mediterranean and Black Sea, at the end of the thirteenth century is one of the most significant occurrences in the history of cartography. Using geodetic and statistical analysis techniques these charts are shown to be mosaics of partial charts that are considerably more accurate than has been assumed. Their accuracy exceeds medieval mapping capabilities. These sub-charts show a remarkably good agreement with the Mercator map projection. It is demonstrated that this map projection can only have been an intentional feature of the charts' construction. Through geodetic analysis the author eliminates the possibility that the charts are original products of a medieval Mediterranean nautical culture, which until now they have been widely believed to be. Map historians, medievalists and all those interested in the history of science. READERSHIP: For more information see http://www.brill.com/products/book/enigma-origin-portolan-charts View full information on http://www.brill.com/

Paper presented at the Second International Workshop on the Origin and Evolution of Portolan Charts, Lisbon, June 2018

Abstract:
The debate on whether or not portolan charts derive from portolans has been ongoing for some 150 years. This paper discusses a comprehensive analysis of the Lo Compasso de Navigare, the oldest portolan containing a complete set of course and distance data covering the Mediterranean and Black Sea. The much-cited analysis by Lanman dates from 1987. Pflederer presented an analysis of a limited subset of data from Lo Compasso de Navigare during the First Workshop on the Origin and Evolution of Portolan Charts in Lisbon in 2016. Both studies were limited in their scope and based on data samples instead of the entire dataset. The study discussed in this paper is comprehensive in the sense that, as far as possible, all locations in the Mediterranean and the Black Sea mentioned in Lo Compasso de Navigare have been identified. That resulted in a dataset consisting of 1330 bearings and distance pairs, large enough to compute reliable statistics and enabled a comparison of nearly every bearing and distance pair in Lo Compasso de Navigare with their true values to be
made. An important aspect of this, discussed in this paper, is the suggestion by James E. Kelley Jr. that “portolans may owe more to portolan charts than vice versa”, which translates into the question whether and if so, to what extent, Lo Compasso de Navigare may have been scaled from one or more pre-existing portolan charts.

Paper presented at the First International Workshop on the Origin and Evolution of Portolan Charts, Lisbon, June 2016.

Abstract:
One of most challenging research elements of medieval Mediterranean portolan charts is the matter of their elusive origin. This does not concern the origin of the surviving physical charts, but the origin of their geometrical information content, consisting primarily of the coastal outlines. Particularly challenging are the charts’ evident accuracy and their good agreement with a Mercator(-like) map projection. Key questions are how these charts were constructed and on the basis of what measurement data. While questions regarding the medieval usage of the charts, the economic aspects of chart construction and their fabrication process clearly fall in the domain of the historian, those concerning the construction technique, accuracy and correspondence with a map projection have a very considerable geodetic component. It is my contention that geodetic aspects have not been given sufficient attention in the research into the origin of portolan charts.
The almost complete absence of historical evidence regarding the charts’ origin requires the researcher to tread carefully and pay adequate attention to the methodological aspects of his or her research. I will discuss several examples where the eagerness to come forward with viable explanations has enticed researchers to step off the narrow path prescribed by the scientific method. Geodetic analysis enables the testing of hypotheses related to the geodetic aspects of portolan charts (construction, accuracy and map projection) with more scientific rigour than would be achievable without such techniques. The key questions regarding the origin of the charts can, in my opinion, only be answered with some hope of success by a fruitful synthesis of history, geodesy and cartography. Researchers from the humanities are faced with a particular challenge to get an adequate understanding of geodetic, mathematical and statistical analysis techniques, in order to be able to understand the results such techniques may yield. Part of this challenge is to understand the importance of the selection of the right method or tool. I will illustrate these issues with the choices I made in my research, which resulted in the surprising and, for the (map ) historical community, unorthodox conclusion that portolan charts are not primitive medieval charts, but instead sophisticated, geodetically-constructed cartographic products.

Portolan charts are realistic and detailed nautical charts of the Mediterranean and Black Seas which appeared suddenly in Italy towards the end of the 13th century. Until now most historians have assumed that these charts are based on measurements of course and distance between ports made by mariners during trading voyages and drawn by a cartographer as if the world were flat. Apart from their evident accuracy, one of the most remarkable characteristics of these charts is their close resemblance to a modern map on the Mercator projection. This study analyses five charts using quantitative geodetic and statistical techniques; this distinguishes it from existing studies, which approach the subject mostly from a qualitative historical perspective. The results are surprising. The charts are demonstrated to be more accurate than has been assumed until now and are shown to be mosaics of five to ten sub-charts, some of which have considerable overlaps. More importantly, the geodetic analysis techniques show that the map projection can only be an intentionally applied design feature of the original charts and not an accidental by-product of the presumed cartographic drawing method, as has been believed until now. The study also shows that portolan charts cannot originate in contemporary Arabic-Islamic civilisation. The consensus view that has existed until now about the origin of portolan charts is thus demonstrated to be incorrect. Their origin must therefore lie considerably further back in time.

Portolan charts are realistic and detailed nautical charts of the Mediterranean and Black Seas which appeared suddenly in Italy towards the end of the 13th century. Until now most historians have assumed that these charts are based on measurements of course and distance between ports made by mariners during trading voyages and drawn by a cartographer as if the world were flat. Apart from their evident accuracy, one of the most remarkable characteristics of these charts is their close resemblance to a modern map on the Mercator projection. This study analyses five charts using quantitative geodetic and statistical techniques; this distinguishes it from existing studies, which approach the subject mostly from a qualitative historical perspective. The results are surprising. The charts are demonstrated to be more accurate than has been assumed until now and are shown to be mosaics of five to ten sub-charts, some of which have considerable overlaps. More importantly, the geodetic analysis techniques show that the map projection can only be an intentionally applied design feature of the original charts and not an accidental by-product of the presumed cartographic drawing method, as has been believed until now. The study also shows that portolan charts cannot originate in contemporary Arabic-Islamic civilisation. The consensus view that has existed until now about the origin of portolan charts is thus demonstrated to be incorrect. Their origin must therefore lay considerably further back in time.