3 ideas
A place is assessed by what it does to a person physically present in it: the approach, the enclosure, the light, the sequence of views, the sounds and the people using it. Reputation, drawings and photographs are set aside, because a building can photograph well and fail in the body, or look like nothing in reproduction and be transformative on site.
Celebrated monuments are often pompous or dead in experience, while anonymous things such as a pub interior, a back street, a railway viaduct or a Victorian parish church frequently give more. Canonical status comes from the history of style and from patronage, not from the lived effect, so a critic has to re-judge each place from scratch and be willing to call a famous building a fraud.
The unit of value is the ensemble rather than the single object: how streets unfold, how spaces open and close, and whether a place keeps its own particular character. Bland, placeless development that makes everywhere feel the same, which Nairn called 'subtopia', destroys this. It also means a mediocre building can be precious in its setting, and a good building can wreck a street.