In 1646, John Blaeu printed a fourth part of the Zeespiegel, bearing the title “Vierde deel der Zeespiegel, inhoudende eene beschryvinge der See-havenen, Reeden, en Kusten van de Middelandsche Schipvaert. Uyt ondervindingen van vele ervaren Zeevaerders by een vergadert, en t’ samengestelt, door Willem Jansz. Blaeu, t’ Amsterdam. Gedruckt by Johan Blaeu, op ’t Water, in de vergulde Zonnewyser. 1646,” or “Fourth Part of the Mirror of the Sea, containing a description of the Harbors, Roadsteads, and Coasts of the Mediterranean Navigation. Collected from the experiences of famous Navigators, and arranged by Willem Jansz. Blaeu at Amsterdam. Printed by John Blaeu on the Water in the gilded Sun-dial, 1646.” There is included in this fourth part the third part of the “Licht der Zeevaert” of 1621, with the arrangement of the contents and the size of the volume somewhat altered. That which is true of certain map publishers in this day, in their attitude toward their own publications, was true of the publishers of these Willem Blaeu maps after his death. So long as there were publishers for them, it was not thought to be necessary to improve them, especially so since John Blaeu, who had succeeded his father in charge of the business, had taken up what he thought to be more profitable printing than the issue of charts for seamen. Other publishers, after the middle of the century, were entering the field, and the Blaeu marine maps in course of time came to be regarded as obsolete. What we may call his first Atlas of land maps appeared in 1631, with the title “Appendix Theatri Ortelii et Atlantis Mercatoris.” It contains maps which had been previously issued, some by himself, many by other map makers, while in numerous instances he left it difficult to decide both date and origin. We know that as early as 1605 he was issuing maps and charts in single sheets, following the example of Ortelius, Mercator, Judeus and others. Baudet, it may be noted, expresses himself as being unable to decide whether the World Map of 1605, referred to in the resolution of the States General of the 23d of April of that year, was of this character, not knowing of the existence of a copy of the map here reproduced in facsimile from that belonging to the Hispanic Society of America. “My belief,” he says, “is that the World Map of 1605 is the Nova totius terrarum orbis geographica ac hydrographica tabula, auct. Guiljelmo Blaeuw,” according to Mercator’s projection, to be found in the “Toonneel des Aerdrycx.”[26] Not unlike Ortelius, Blaeu often selected for addition to his own original land maps the best which he found it possible for him to use, redrafting them on a scale to fit his own Atlas. In general, he greatly improved their character by his own re-engraving, giving us maps of superior excellence in line, in letter, and in ornamentation. He was not unmindful of the high favor in which the Atlases of Ortelius and of Mercator were held.