Right. For example I know the area around Temple Church in London really well - for a few years I used to walk through it twice daily on my commute. So when there was all the fuss about the Da Vinci Code I decided to read it for myself to make up my own mind, and terrible as it was the thing that probably annoyed me the most was he gets the geography of those streets wrong. It wasn't changed because the change helped the plot or anything like that - it was just wrong because he didn't care at all about getting details right. It was so _unnecessary_ an error it really drove me nuts.

I love Foucault's Pendulum. I always thought it's a fun sideswipe at the literary Foucault also, who with Derridas is so deliberately impenetrable there are a lot of parallels with the charlatans in the novel.

Does a writer have to be intimately familiar with every location they describe in their books? I know some are, and it's great when they get stuff right, but I don't think it's really that big of a problem when they don't.

Although I'm also reminded of how movies get things hilariously wrong in ways that can't be an accident. When I was young, there was a Dutch thriller called Ansterdamned, about a scuba diving murderer moving through the canals of Amsterdam. Lots of locations I recognise. Then there's a massive speedboat chase, and suddenly they're going through a famous and unmistakable canal in Urecht. Fun movie, but the sudden teleport to Utrecht is a bit jarring.

I agree they don't have to be, but a sense of authenticity of location can really add to the atmosphere of a novel. For example, in "Mrs Dalloway", you can literally retrace the steps of Mrs Dalloway through St James' park and St James' and on to Bloomsbury. The descriptions are incredibly precise and totally accurate. Likewise people walk through Dublin visiting the exact scenes depicted in "Ulysses".

Another example (slightly obscure) from London is "The Book of Dave" by Will Self, which is partly set in a post-apocalyptic future. The geography is very thoughtfully handled, but in this future the Thames has flooded and lots of London is underwater. Part of the fun is figuring out which bits of present London they are referring to when they talk about landmarks etc which survive[1].

Now it's fair to say all those examples are shooting a lot higher-brow than Dan Brown, but another example more similar in genre aesthetic to Dan Brown would be John LeCarre's "Smiley" novels (eg "The spy who came in from the cold" etc). To the extent I know the locations in the ones I have read, they seem to me very authentically described, which greatly enhances my sense of immersion in the atmosphere.

[1] eg "centrul stack" I'm pretty sure is the wreck of the Centerpoint Building, now an empty shell filled with seabirds.

Lee Child, in his Reacher novel “Night School”, has a major part of the plot being played out in Hamburg’s “HafenCity” quarter. Reading it, you’re rather sure that the author has visited Hamburg and has traced himself the steps of his fictional character.

Only problem: the novel plays in 1997, a time, when the HafenCity quarter didn’t exist. Back then it was Hamburg’s old free port area, behind a customs border, not the “normal” city quarter as described. The current quarter is in effect a new development, which didn’t exist in 1997.