The houses that Emily grew up in and lived in after she came back from Washington are real houses, though not at the location in the stories.
My mother worked for MIT Press at a time when the press was publishing a series of book on the architecture of Cambridge.
I spent a week one summer looking for the buildings I wanted to use. I found the locations I wanted and then went to visit them. I walked from one to the other as my character did. I was surprised to find that Dana Street had a slope when I remember it as being flat.
I spent so much time trying to figure out what was inside "The Villa" I thought I might be arrested for loitering. The "Cottage" was a bit easier to scope out. It really is on a busy street corner, but I moved it to a more sedate location further up Dana Street.
The church she and her family attended still stands. My mother was a member.
On the other hand the area she lived and worked in Washington have been cleared and rebuilt. I have a photo of the back of what would have been the office building. The church she attended in Washington move its location twice. The newest building postdates her return to Cambridge. Never the less, I knew where everything had been and I walked all those distances as well. I went to see the Dunkin' Donuts where the church had stood, the new office building that was where Lawrence Research had been.
The house I chose for them to purchase when they had enough money to move out of Mrs. Johnson's place is (I think) the house Mathew Brady lived in on Maryland Avenue. I have seen it only in photographs, since the whole area has been redeveloped.
I have to do and see all the things my characters do and see. I always have a real location in mind even if the fictional location is vague. Maybe I should have a guess the location game in the back of the book.