That’s a goddamned stretch if ever there was one. SoCal is more or less a recognizable region in California, and does indeed have almost 24M people, but nobody sane would call it a megalopolis without some weird agenda I can’t quite figure out.
Los Angeles is a city of about 3.9M. LA County is well, apparently experiencing some population decline because last I checked this was a little over 11M, but apparently as of 2023 is around 9.6M. If you count all the urban areas that touch, are surrounded by or very very close by without driving out into the bloody desert, “greater” LA, 18.4M is probably a reasonably close figure. Some of what’s on Wikipedia’s map is a stretch though. The further East you go, the more rural California gets until you’re either in Clark County or Arizona.
San Diego though is by no means part of that. It’s a large city in its own right and going downtown to downtown, you’re talking at least between 2 and 2.5 hours driving. You can also just fly, on a regular commercial airline.
A megalopolis isn't characterized by a placename and an airport. It's characterized by continuous development. You can drive from Ventura to Yucaipa to to Temecula to Rosarito Beach in Mexico, and the only time you'd need to get a mile away from of high-density development is 5 miles of I-15 in a mountain pass, or 10 miles of coastal highway, both to span the Santa Ana Mountains (property of the US Forest Service / Cleveland National Forest for the most part).
The Los Angeles Conurbation is about to swallow the northern Imperial Valley as well, because the I-10 corridor is made up of flat sandy dirt that could be a suburban back yard.
> A megalopolis (/ˌmɛɡəˈlɒpəlɪs/) or a supercity,[1] also called a megaregion,[2] is a group of metropolitan areas which are perceived as a continuous urban area through common systems of transport, economy, resources, ecology, and so on.[2] They are integrated enough that coordinating policy is valuable, although the constituent metropolises keep their individual identities.[2]
2 hours driving, in the US, is a natural distance for complementary but distinct cities to form. NYC/Philly/DC, SF/San Jose, LA/SD.
How is Tijuana, Mexico part of the Southern California megalopolis? That doesn't make much sense and I wouldn't consider San Diego part of the LA/OC megalopolis either, especially since there's a mountain range separating them with not much civilization in between.
Either way, we've got enough people to invade Australia and no Kokoda Trail is going to help them this time! We must get a plan to Gavin Newsom’s desk at once. The Koala mines will be ours!
The only thing that stops San Diego from being connected to LA/OC is the Camp Pendleton Marine base for about 7 miles. Basically you can go from Tijuana all the way up the coast to LA and only have that stretch not populated with civilians.