During his training Doctor Strange gets told that there are 3 important sanctums spread around the world to serve as protection against extra-dimensional powers trying to take over the world. And indeed he later has to protect exactly those three temples against attacks from Kaecilius who tries to enable Dormammu take control of our dimension.
The way they explained the significance of the sanctums, it sounded like they were strategically placed at locations of naturally strong mystical powers. This in turn made me wonder why they also coincided with places of very high importance to the real world, i.e. Hong Kong, London and New York. I could understand this for London and maybe Hong Kong due to their longer history and possible mystical significance back in the "old" days, but less so for the about 400 years old New York City (unless there's a longer Native American significance to that actual location I'm unaware of).
But then someone pointed out that he understood the places were only chosen because of their strategic locations around the globe (and maybe influenced by their secular importance) without bearing a special magical history at all. But even then this would still mean that the sanctums (or at least the NYC one) couldn't be much older than about 300-400 years, while the whole sorcerers' society seemed significantly older (if I remember correctly, the Ancient One was said to be about (or more than?) 1,000 years old).
So what was first, the magical significance of those three places or the sanctums erected there? Is there any more information about the history of those buildings and the reasons for their specific locations, be that in the comic sources or any other official material? Or is this explained more thoroughly and conclusively in the actual movie than my memory recalls?