Enigma of the Origin of Portolan Charts

Roel Nicolai, PhD, MSc (1953) is Principal Geodesist with Shell. This book is a revision of his PhD thesis and his first publication in the area of the history of science and cartography.

• Preface xiAcknowledgements xivList of Illustrations xv1. Introduction 11.1 The Origin of Portolan Charts: Research Challenges 11.2 Objective and Scope of this Book 41.3 Four ‘Pillars’ 52. Key Characteristics of Portolan Charts 112.1 Preamble 112.2 Distinguishing Characteristics 122.3 Disputed, Unclear and Unsatisfactorily Explained Aspects of Portolan Charts 193. Existing Hypotheses on the Origin and Construction Method of Portolan Charts 443.1 Scholarly Views on the Origins Debate 443.2 Ideas on Antique Origins 463.3 Hypotheses on Medieval Origins 523.4 Hypotheses on Portolan Chart Construction 593.5 Plane Charts versus Plane Charting 633.6 The Rotation Angle 763.7 Methodological Considerations 824. Cartometric Analysis; Methodology and Existing Research 864.1 Introduction 864.2 Quantitative Analysis Methods – A Conceptual Classification 924.3 Existing Cartometric Studies 1034.4 Chart Selection 1164.5 Cartometric Analysis Approach 1195 Cartometric Analysis of Five Charts 1335.1 Carte Pisane 1335.2 Anonymous Genoese Chart (Ricc 3827) 1385.3 The Ristow-Skelton No. 3 Chart (RS-3) 1435.4 The Dulcert 1339 Chart 1475.5 The Roselli 1466 Chart 1485.6 Analysis of All Results 1525.7 How Difficult is It to Make an Accurate Map? 1955.8 Conclusions 1976 The Relationship between Portolans and Portolan Charts 2016.1 Introduction 2016.2 Existing Research 2026.3 A New Analysis of Lo Compasso de Navegare 2166.4 Summary of the Analysis 2766.5 Conclusions 2837. Constraints on Shipping and Navigation in the Medieval Mediterranean 2857.1 Introduction 2857.2 The Physical Conditions of the Mediterranean 2867.3 Medieval Ships 2987.4 An Accuracy Model for Medieval Mediterranean Navigation 3117.5 Conclusions 3228. The Map Projection, Artificial or Intentional? 3248.1 Introduction 3248.2 A Priori Geodetic Objections 3278.3 Existing Research 3318.4 Conceptual Workflow and Test Criteria 3358.5 Design Principles for a ‘Medieval’ Geodetic Network 3378.6 Introductory Information on Geodetic Network Analysis 3418.7 Network Definition and Analysis 3488.8 Network Adjustment #1 (Accuracy) 3518.9 Network Adjustment #2 (Shape) 3588.10 Summary of the Geodetic Analysis 3678.11 Accuracy Enhancement by Averaging in the Context of the History of Science 3698.12 Conclusions from This Chapter 3769. Navigational Practices in the Twelfth and Thirteenth Centuries 3779.1 Drawing up the Interim Balance 3779.2 Navigational Tools: Charts & Dividers, Needle & Star 3799.3 The Toleta de Marteloio 3829.4 The Mathematical Seaman 3889.5 Early Time Measurement at Sea 3919.6 Distance Measurement at Sea 3929.7 Bearing Measurement – The Mariner’s Compass 3979.8 Conclusions 41310 An Arabic-Islamic Origin of Portolan Charts? 41410.1 Introduction 41410.2 Ibn Fadl’allah’s Map – The ‘Mamun Geography’ 41510.3 Progress in Astro-geodetic Position Determination 41710.4 Sezgin’s Hypothesized Construction Method of Portolan Charts 42010.5 Further Arguments Presented by Sezgin for an Arabic-Islamic Origin of Portolan Charts 42311. Conclusions 42911.1 Recap of Conclusions by Chapter 42911.2 The Four ‘Pillars’ of the Medieval Origin Hypothesis 43311.3 Key Conclusions from this Study 43712 Synthesis 43912.1 Introduction 43912.2 The Appearance of Portolan Charts in Medieval Italy 43912.3 Remaining Issues 44212.4 Recommendations for Further Research 450Appendix A: The Historical Setting of the Emergence of Portolan Charts 453A.1 The Medieval Mediterranean – Relevant Historical Aspects 453A.2 The Awakening of Europe 454A.3 The Italian Maritime Republics and Aragon 455Appendix B: Calculation of the Length of a Rhumb Line 467B.1 An Arbitrary Line on a Sphere 467B.2 The Line in a Specified Direction on a Sphere 468B.3 Mercator Sailing – How to Plot Sailed Distance on aChart? 469Appendix C: The Plane Charting Examples from Chapter 2 471C.1 Dimensions of the Earth 471C.2 The Routes from Livorno to Dellys 471C.3 Four More Arbitrary Routes 479Appendix D: Accuracy Model for Medieval Navigation 483D.1 Introduction 483D.2 Along-course Accuracy 484D.3 Cross-course Accuracy 490Appendix E: Cartometric Analysis Details 495E.1 Coordinates of Identical Points 495E.2 Preprocessing – Wind Rose Analysis 498E.3 Main Cartometric Analysis 499Appendix F: Reliability of the CALS7k.2 Archaeomagnetic Model 504Appendix G: Is the Map Projection Accidental? A Statistical Analysis 508G.1 Preamble 508G.2 Statistical Basis 508G.3 Test Results 510G.4 Discussion 515G.5 Conclusion 516Appendix H: The Preface of the Liber de existencia riveriarum 517Bibliography 520Index 538