Los Francisco or San Angeles?
Part of the reason Hitchcock lasted so long is that nobody could really predict what he was going to do -- or figure out why he did it when he did.
Example: after making "Psycho" with the greatest thriller musical score of al time, Hitchcock makes "The Birds" -- with NO music at all.
Hitch kept it up right to his last film: "Family Plot."
Look at the films in the years before it: Frenzy is set in London; Topaz in Paris, Cuba, the U.S. and Copenhagen; Torn Curtain in East Germany; Marnie in Philadelphia and Maryland; The Birds in Bodega Bay, Psycho in Arizona and California, North by Northwest all over the place in America, and Vertigo in San Francisco. Many Hitchcock movies were set in New York City; The Trouble With Harry in Vermont, etc.
But where, oh where, is Family Plot set?
Hitchocck never really says. And he did that on purpose.
He told interviewers, "Oh, I think its a city on the East Coast somewhere." We hear mention of a small town called "Barlow Creek," but the big city is never mentioned.
Actual filming was on a mix of Los Angeles and San Francisco locales: the bishop is kidnaqpped from Grace Cathedral in San Francisco (a tiny bit of which I think is visible in "Vertigo" behind James Stewart when Scottie is looking at the Elster apartment building on Nob Hill); and Adamson's townhouse is in San Francisco, too.
But Blanche's bugalow is in Los Angeles, as is the cemetary. The runaway car sequence was filmed in the sparse "Angeles National Forest" east of LA.
And Hitchcock mixed and matched it all together into a seamless whole.
Why?
Let's guess:
1. "Vertigo" had been one of the most unforgettable tours of San Francisco ever put on film; Hitchcock didn't want to compete with one of his greatest films.
AND/OR
2. Hitchcock felt that San Francisco had been in too many movies (Vertigo, The Birds, Bullitt, Dirty Harry, What's Up Doc to name a few), so was now "cliche." Moreover, Hitchcock never really wanted to set a movie in "unmysterious" Los Angeles ("Chinatown" aside.) And he didn't have the budget or health to film "Family Plot" in some other city like New York City or Seattle or New Orleans, etc.
The result is odd, indeed. If you know San Francisco and Los Angeles, it is just plain weird to see the two cities mixed up like this.
If you don't know the cities, you end up with perhaps the most oddly set of all Hitchocck American films:
It's a movie that takes place... nowhere.