{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,8,15]],"date-time":"2025-08-15T02:45:59Z","timestamp":1755225959398,"version":"3.43.0"},"reference-count":27,"publisher":"University of Toronto Press Inc. (UTPress)","issue":"2","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Cartographica"],"published-print":{"date-parts":[[2025,7,1]]},"abstract":"<jats:p> Following the introduction of the marine compass in Europe during the last decades of the thirteenth century, an intimate \u2013 and sometimes problematic \u2013 relationship between the Earth\u2019s magnetism, navigation and nautical cartography developed. Because charts were constructed using uncorrected compass courses collected by pilots at sea, their coastlines often appeared distorted, reflecting the effect of magnetic declination. Although the phenomenon was acknowledged by the late fifteenth century, serious consideration of its effect on charts was slower to come. This status quo was first put in question after Magalh\u00e3es and Elcano\u2019s voyage to South-East Asia (1519\u20131522), when it was realized with surprise that, contrary to contemporary nautical cartography, the coveted Spice Islands were not situated in the Spanish hemisphere, according to the terms the Treaty of Tordesillas. The issue triggered a long discussion between politicians, cosmographers, chart-makers, and pilots, not only about the necessity of correcting the mistake but also about how navigation should be conducted and charts made. At the core of the debate was the inescapable clash between the contemporary cartographic model, based on routes, and the Ptolemaic map prescriptions, based on geographical coordinates. This article explores how nautical cartography responded to such issues. By analysing the geometry of Africa in early modern charts of different origins, the author first clarifies whether and when they began to be corrected for magnetic declination and then offers hypotheses about how and why those changes were made. The results indicate that rather than correcting the orientation of coastlines on charts to conform with either true geographical directions or up-to-date compass readings, the adjustments involved astronomical measurements of longitude. <\/jats:p>","DOI":"10.3138\/cart-2024-0033","type":"journal-article","created":{"date-parts":[[2025,8,13]],"date-time":"2025-08-13T22:14:15Z","timestamp":1755123255000},"page":"45-61","source":"Crossref","is-referenced-by-count":0,"title":["Magnetism, Navigation, and Cartography in the Early Modern Period: An Elusive Relationship"],"prefix":"10.3138","volume":"60","author":[{"given":"Joaquim Alves","family":"Gaspar","sequence":"first","affiliation":[{"name":"Department of History and Philosophy of Sciences \/ Faculty of Sciences \/ University of Lisbon \/ Lisbon \/ Portugal"}]}],"member":"1696","reference":[{"key":"r1","volume-title":"Contribui\u00e7\u00e3o das navega\u00e7\u00f5es do s\u00e9c. 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Jo\u00e3o de Castro, Vol. I","author":"Castro Jo\u00e3o de.","year":"1968"},{"key":"r5","volume-title":"Obras Completas de D, Jo\u00e3o de Castro","author":"Cortes\u00e3o Armando","year":"1982"},{"key":"r6","volume-title":"A Marinharia dos Descobrimentos","author":"Costa Avelino Fontoura da","year":"1983","edition":"4"},{"key":"r7","volume-title":"The Diario of Christopher Columbus\u2019s First Voyage to America 1492\u20131493","author":"Dunn Oliver","year":"1989"},{"key":"r8","unstructured":"Gaspar, Joaquim Alves. 2010. From the Portolan Chart of the Mediterranean to the Latitude Chart of the Atlantic: Cartometric Analysis and Modeling. Unpublished doctoral dissertation. Universidade Nova de Lisboa."},{"key":"r9","doi-asserted-by":"crossref","first-page":"35","DOI":"10.14195\/978-989-26-0764-1_3","volume-title":"Hist\u00f3ria da Ci\u00eancia Luso-Brasileira. 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A Social History of the Mercator Projection","author":"Monmonier Mark","year":"2004"},{"key":"r20","volume-title":"Instru\u00e7\u00f5es N\u00e1uticas para os Pilotos da Carreira da \u00cdndia nos Come\u00e7os do S\u00e9culo XVII","author":"Mota Avelino Teixeira da","year":"1974"},{"key":"r21","volume-title":"Obras, Vol. I: Tratado da Sphera; Astronomici Introductorii de Spaera Epitome","author":"Nunes Pedro","year":"2002"},{"key":"r22","volume-title":"Obras, Vol. IV: De Arte Atque Ratione Navigandi.","author":"Nunes Pedro","year":"2008"},{"key":"r23","volume-title":"De Rebvs Regis Emmanuelis Regis Lusitaniae","author":"Os\u00f3rio Jer\u00f3nimo","year":"1571"},{"key":"r24","first-page":"115","volume-title":"Estudos de Hist\u00f3ria da N\u00e1utica e das Navega\u00e7\u00f5es de Alto-Mar","volume":"2","author":"Pereira Jos\u00e9 Manuel","year":"2013"},{"key":"r25","first-page":"38","volume":"111","author":"Tyacke Sarah","year":"2007","journal-title":"IMCoS Journal"},{"key":"r26","first-page":"1722","volume-title":"History of Cartography","volume":"3","author":"Tyacke Sarah","year":"2007"},{"key":"r27","volume-title":"The Art of Navigation in England in Elizabethan and Early Stuart Times","author":"Waters David W.","year":"1958"}],"container-title":["Cartographica"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/utppublishing.com\/doi\/pdf\/10.3138\/cart-2024-0033","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,8,13]],"date-time":"2025-08-13T22:14:26Z","timestamp":1755123266000},"score":1,"resource":{"primary":{"URL":"https:\/\/utppublishing.com\/doi\/10.3138\/cart-2024-0033"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2025,7,1]]},"references-count":27,"journal-issue":{"issue":"2","published-print":{"date-parts":[[2025,7,1]]}},"alternative-id":["10.3138\/cart-2024-0033"],"URL":"https:\/\/doi.org\/10.3138\/cart-2024-0033","relation":{},"ISSN":["0317-7173","1911-9925"],"issn-type":[{"value":"0317-7173","type":"print"},{"value":"1911-9925","type":"electronic"}],"subject":[],"published":{"date-parts":[[2025,7,1]]}}}