Luis A. Robles Macías (lroblesm@uoc.edu) is employed as an engineer at Total, a major energy group. He is currently pursuing a Masters degree in Information and Knowledge Management at the Universitat Oberta de Catalunya.
Date of Publication: May 24, 2010
Abstract: Previous cartographic studies of the 1500 map by Juan de La Cosa have found substantial and difficult-to-explain errors in latitude, especially for the Antilles and the Caribbean coast. In this study, a mathematical methodology is applied to identify the underlying cartographic projection of the Atlantic region of the map, and to evaluate its latitudinal and longitudinal accuracy. The results obtained show that La Cosa’s latitudes are in fact reasonably accurate between the English Channel and the Congo River for the Old World, and also between Cuba and the Amazon River for the New World. Other important findings are that scale is mathematically consistent across the whole Atlantic basin, and that the line labeled cancro on the map does not represent the Tropic of Cancer, as usually assumed, but the ecliptic. The underlying projection found for La Cosa’s map has a simple geometric interpretation and is relatively easy to compute, but has not been described in detail until now. It may have emerged involuntarily as a consequence of the mapmaking methods used by the map’s author, but the historical context of the chart suggests that it was probably the result of a deliberate choice by the cartographer.
Keywords: maps; cartography; Juan de la Cosa; cartographic projections; obliquity; latitude; ecliptic; Tropic of Cancer; spherical trigonometry; gnomonic projection; unnamed projection; Christopher Columbus
CONTENTS
1. Introduction: The Map of Juan de la Cosa
2. The Problem of Latitude in the La Cosa map
3. Identifying the underlying cartographic projection
—Methodology
—A New Interpretation for La Cosa’s ‘Cancro’ line
—Mathematical Derivation of Candidate Projections
4. Gnomonic Projection
5. Unnamed Projection
—Equations
—Geometric Interpretation
—Cartographic Properties
—History
6. Comparison with the La Cosa Map
—Caribbean
—South America
—West Africa and Atlantic islands
—Equatorial and Southern Africa
—Europe and the Mediterranean
—Northern Regions
—Overall View
7. Discussion
—Just a Coincidence?
—Involuntary Emergence
—Spirit of Innovation in Cartographic Projections
—Determination of Geographical Coordinates
—Trigonometry
—The Ecliptic on Maps
8. Conclusions and Open Questions
Acknowledgements
Annex 1: Control Points
Annex 2: Mathematical Annex
Notes
