Sometimes you get sent something which is Exactly What You Need that you kind of stop and look around because this kind of thing just doesn't happen that often.
Like you are trying to parse the information in a half dozen guidebooks and histories and websites and piece it all together and it's becoming a jumble in your head . . . and then you get Exactly What You Need.
Which in this case is a clear, concise guide to a very large selection of notable works of architecture in the Paris area, broken down by arrondissement/region and clearly stating the approximate construction years for each . . . plus every renovation large and small, from massive reconstructions to bored nobles and architects fiddling with facades and garden layouts.
(I say selection because the foreword is careful to use that language, but it seems pretty comprehensive to me; the foreword has the feel of that academia defense-best offense strategy of preempting the architecture nerd who wrote his thesis on that notable WC in the 4th arrondissement and why didn't you include that? Hmm? HMM?)
So someone who, ahem, might be trying to design a kind of self-guided Ancien Regime tour of Paris can go from arrondissement to arrondissement and say to herself, I should really see buildings 3, 17, and 20 here, and 1 and 5 here, but skip 6 because even though it's technically 18th century it's been remodeled into some other beast entirely . . . and so on. In one book. Without recourse to Google, Wikipedia, iPhone apps, French tourism sites, or that friend of a co-worker's who went to a cool place that looked like a house in Dangerous Liaisons, can't remember the name but you really have to go there!
Plus it is stinkingly well-designed in a Germanic way: no frills, sans serif, small but clear b&w illustrations. It fits well in the hand, thick and weighty yet compact. I like it so much it might even have to fly over with me. It feels authoritative, in a paternal, comforting way; it says keep me in your hand and you will make no mistakes.