Which 1570 atlas by Abraham Ortelius is often called the first modern atlas?

Abraham Ortelius’s 1570 atlas often called the first modern atlas was Theatrum Orbis Terrarum.

First published in Antwerp on 20 May 1570, the Theatrum Orbis Terrarum—“Theatre of the World”—brought maps of the known world together in a coordinated, commercially produced volume. Ortelius did not draw every map himself. Instead, he selected, adapted, and standardized material from numerous cartographers, presenting the sheets in a consistent format with accompanying descriptions.

Its importance lay in organization as much as discovery. Earlier map collections existed, but Ortelius created a unified reference work arranged by regions and supported by a bibliography identifying many of his sources. That source list, the Catalogus Auctorum, preserved the names of cartographers whose work might otherwise have been forgotten.

The atlas rapidly expanded through revised editions and translations. Its first edition contained 53 maps, while later editions added more maps, text, and references; by 1612, the work had reached 31 editions. It is sometimes confused with individual portolan atlases or ancient works such as Ptolemy’s Geographia, but those belong to different mapping traditions and do not carry the same claim to a modern, standardized atlas.