JF Ptak Sciene Books Part of the series on The History of Blank, Empty and Missing Things.
The influence of economic strategy seems to be the Old Red Sandstone of the geology of life on this planet, and sometimes it reaches right into cartography, expressing itself in unusual ways. Such may be the case with the creation of the idea of California beign an island.
In general, much of the vast expanse of blankness of the continent in the 16th and 17th century was hidden under ornate Baroque cartouches and their encumbrances, which was a tried-and-true method of taking up space on a map where you didn't (a) really know what was their and (b) didn't want to make stuff up to fill in the white space. By necessity most of North America was unknown to cartographers at this time because, well, there was no reliable information to work with. The far reaches of the middle North American western coastline enjoyed a history of connectivity with the large land mass that exists east of the Gulf of California, the region known today as "california" being connected to the rest of the continent from the early 16th century.
About 116 years later, though, cartographic thinking on part of the coast changed. Antonio de la Ascensíon is credited with first giving flight to the idea that the California Peninsula was in fact an island--and so, beginning in 1620, California would frequently make guest appearances on maps as an island. (Fray Antonio was born in Salamanca in 1573/4 and studied there and at the College of Pilots in Seville; he was ordained in the Order of Discalced Carmelites, and sent off to Mexico. As a cosmographer he accompanied Sebastian Vizcaino (1548-1624) on his expedition to California to find a good port for Spanish galleons coming from Manila, which is when Antonio produced his diaries with the famous island maps1.) This map was created during a period where there was heavy competition for trade routes and geographical knowledge was actual currency, so there was some amount of cartographic information that was proprietary. When the abbot's map was lost to/and recovered by the Dutch, the changes that were made to California were codified and published--the Spanish thought it not necessary to correct the misinformation. Perhaps. In any event, it seems plausible that the Spanish crown had no interest in involving itself with what may or may not have been the loss of proprietary information, and so let the island business slide. Until1751, when the King of Spain issued a proclamation saying that California was indeed not an island.
This practice continued to about 1747, when there was more than ample evidence to suggest that the island status of California was erroneous--still, it took several decades for the last of the island-maps to make its appearance.