Maps of the Amazon are largely terra incognita (unknown land) before the 1800s. Although the main river was first explored in the 1540s, accurate maps were not made until the late 1800s when the Western powers realized there was something of value there, namely rubber. Part of the reason for improvement is that mapmakers improved their skill, and moved from the realm of artistry to science. Another reason is that over time the Amazon region was more widely explored, so mapmakers could compile quite good maps of small areas into maps of the larger Amazon basin. Today, these old maps are collector's items, costing from a few tens to thousands of dollars.