Someone on this forum has once mentioned being able to imagine the places described in the book as similar places from his own life matched up with the character's age. He also said that he gradually lost this ability as he got older.
I have something very similar, and this has also changed as I got older. As a child (10 years old or so), I read a lot, and tended to imagine every place being described as some place I knew from my own life. This is not to be taken that I imagined the place exactly the way I knew it in reality, only that I modeled my imagined place on the real one in some respects. For example, I remember that I imagined the throne room of Shaddam IV similar to a classroom in my school. Of course it wasn't exactly majestic or throne room-like or anything, but it was the best I could come up with. I figured everyone worked like this so I didn't really mentioned it to anyone. (As of now, I have absolutely no idea about the prevalence of this experience.)
Later, this did not disappear, but changed altogether. About since my high school years, whenever I have read something, either fiction, textbook, whatever, I "projected" myself to some place in reality, and somehow "felt myself" to be there while I read about that subject.
The curious thing about this is that it is subject-sensitive. I could even draw a map of "projection points" and their respective subjects. E.g. the projection point for Asimov is located inside my old high school building. The projection point for LOTR is at a street crossing in my city. Ubuntu's projection point is near a bus stop on a large road in the same city. Sometimes, it does not even have to be reading, it is enough if I concentrate on any matter enough. The projection points are largely conserved, that is, when I started to re-read Asimov, I immediately projected to the same place in my high school I did when I read the books first. New projection points are not randomly formed, however. They are likely to be situated to those places I visited frequently in the last few weeks. Some of these places do not even exist anymore, e.g. the point for the Linux kernel is in at an old marketplace that has since been demolished.
This "projection" happens practically any time I enter the world of a book or immerse myself completely in any activity, but when I finish, it is very hard to recall if the projection happened, very similarly to the way it is hard to recall dreams. Because of this, I suppose the mechanism behind the phenomenon is similar to dreaming; perhaps those parts of the brain that are unused while reading go into a state similar to REM sleep. (Good thing I have friends at an EEG lab, this could actually be checked!)
I have not really had the courage to talk about this to anyone. I would like to know if anyone experiences anything similar, or I am alone with this condition.
Possible clues: I am not psychotic, and have never been. I am a suspected bipolar II. I have synesthesia.