Looking at statisticalatlas, one can make a core area that contains the following census county divisions:
Los Angeles CCD 2,574,176 (includes Beverly Hills, Culver City, West Hollywood)
San Fernando Valley CCD 1,840,994
Santa Monica 92,247
Total population 4,507,417
These CCDs must contain the majority of L.A.'s Jewish population.
https://statisticalatlas.com/county/...nty/Population
The federation area would also include South Bay, Torrance, Inglewood, Compton and East Los Angeles (areas that have few Jews).
(I think this may be inspiration for a thread on what constitutes the core of L.A.)