The fair place to meet is Oklahoma City, OK — the city closest to the midpoint of Indianapolis and San Diego. From the farther side that’s about 23 hr 52 min of driving.
Recommended midpoint
Oklahoma City, OK
From Indianapolis
14 hr 26 min
688 mi to Oklahoma City
From San Diego
23 hr 52 min
1,138 mi to Oklahoma City
Indianapolis has the shorter trip; the split is off by about 9 hr 26 min. The alternatives below can even it out. Indianapolis and San Diego are about 1,785 miles apart.
Indianapolis and San Diego are about 1,785 miles apart by road. Split the difference and you arrive near Oklahoma City, the city closest to the halfway point between them. That puts roughly 14 hr 26 min of driving on the Indianapolis side and 23 hr 52 min on the San Diego side — the fairest single meeting point among the cities near the middle.
Over this distance most people will fly rather than drive the whole way. Oklahoma City still makes a fair, central place for Indianapolis and San Diego to converge, splitting the travel instead of asking one side to cross the country.
If Oklahoma City doesn't have what you're after, Albuquerque and Denver are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Indianapolis and San Diego.
Oklahoma City, often shortened to OKC, is the capital and most populous city in the U.S. state of Oklahoma. It is the 21st-most populous U.S. city and 8th largest in the Southern United States, with a population of 681,054 at the 2020 census. Read more →
Indianapolis, colloquially known as Indy, is the capital and most populous city of the U.S. state of Indiana and the county seat of Marion County. Indianapolis is situated in the state's central till plain region along the west fork of the White River. Read more →
San Diego is a city on the Pacific coast of Southern California, adjacent to the Mexico–United States border. It is the eighth-most populous city in the U.S. Read more →
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.
Estimates use straight-line distance and typical road speeds; real drive times vary with route and traffic.