[Mithadan]

I generally agree with Galadriel. The Ainur, collectively, have an understanding of the "true" history, nature and creation of Arda. Individually, each Ainu has some degree of knowledge about Arda, generally, and specifically about their "area of interest." Thus Yavanna and her people know about growing things, Aule knows about the stuff of Arda and creating tools and things of use or beauty. Ulmo knows of the seas and waters. Manwe and Melkor were the real generalists.

The Istari were, of course, of the Ainur. They would share in the knowledge of history, nature and creation of Arda. Individually, they would have greater knowledge of areas relating to their affiliations. Saruman was a Maia of Aule, if I recall. He knew of machines and tools. Thus his interest in the history and creation of the Rings of Power. Radagast's interest and knowledge was of the animals. Gandalf was affiliated variously with Manwe, Lorien and Nienna. His knowledge was more general, but with an emphasis upon sympathy for and inspiring of the people of Middle-Earth.

However, it would seem that none of the Istari had any especial knowledge of Third Age Middle-Earth, it's geography and populations. They did not, for example, have an understanding or innate familiarity with the layout of Middle-Earth; they had no built in map. Thus Radagast had no idea where the Shire was (nor did Sauron, who was also a Maia). They had to learn about Middle-Earth, via exploration or study.