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Ortelius, a major figure in cartography, is renowned for his groundbreaking work in mapmaking. His most notable achievement is the creation of the first modern atlas, Theatrum Orbis Terrarum, published in 1570. This comprehensive collection of maps revolutionized the field of cartography and set the standard for future mapmakers. Ortelius' contribution to the study and understanding of geography has left an indelible mark on the history of the discipline.