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The network move of "Supergirl" this season made it easier to pull off the four-show crossover that's about to dominate The CW.

It's not just "Supergirl's" move from CBS to The CW, where it joined "The Flash," "Arrow" and "DC's Legends of Tomorrow." The "Supergirl" production moved from Los Angeles to Vancouver, where it joined the other four shows.

"It sure helps with the logistics," said executive producer Greg Berlanti, whose team writes and produces all four shows. "We don't have to worry about Melissa [Benoist] flying to Canada or anybody else flying down [to Los Angeles]."

Last season, "Flash" star Grant Gustin went to L.A, for a March episode of "Supergirl" — arguably the series' best first-season installment. And it certainly didn't hurt that Gustin and Benoist had instant chemistry.

"We couldn't wait to do it again," Berlanti said.

Only this time, it's crossover-times-four.

"There will be a piece of it that touches 'Supergirl,' but it will primarily start in 'The Flash' episode," Berlanti said.

It's not giving anything away to say that, at the end of Monday's "Supergirl" episode (7 p.m., CW/Ch. 30), the Flash shows up on Supergirl's Earth and asks her to help fight off an alien invasion.

Yes, The Flash and Supergirl are on different Earths in different dimensions.

Fortunately, in order to travel from one dimension to another, "We just have to write it," Berlanti said with a laugh. "And pay for a few special effects."

The story really gets going on Tuesday's "Flash" episode, continues on Wednesday's "Arrow" episode and concludes in Thursday's "DC's Legends of Tomorrow" episode (all 7 p.m. on CW/Ch. 30).

Those three shows all exist in the same dimension.

Even if you don't watch all four shows, Berlanti and his team promise you won't be lost. They know that some fans may watch one, two or three of the series, but not all of them.

If the four-show crossover event persuades "Supergirl" fans to start watching "Arrow," then "That's terrific," Berlanti said. "But I wouldn't say that's our goal."

He wasn't being disingenuous. Obviously, he'd love to have more viewers for every one of his shows. (Including "Blindspot" over on NBC.)

But what prompted the "Supergirl"-"Flash"-"Arrow"-"Legends" crossover was — "We love these shows and we love these characters," said Berlanti. "We're doing it because we want to see these characters together."

They're doing it to entertain themselves. Which is almost always the best way to go about making a TV show. Better to make the show you want to see yourself, not the show you're guessing other people want to see.

In addition to the five shows he currently has on the air, Berlanti has a sixth — the "Archie" comics-inspired "Riverdale" — which debuts Jan. 26 on The CW.

Since he took over running "Dawson's Creek" 16 years ago, when he was just 28, he's had successes like the made-in-Utah "Everwood" and "Brothers & Sisters." Not all of the 17 shows he's produced have been hits. But a lot of the misses have been great shows that deserved longer lives — shows like "Jack & Bobby," "Dirty Sexy Money," "Eli Stone," "Political Animals" and "Golden Boy."

"It would be hard to work on a show I didn't like," Berlanti said.

And with the exception of the oddly out-of-character "Mysteries of Laura," it's hard not to like any of Berlanti's shows.

Scott D. Pierce covers television for The Salt Lake Tribune. Email him at spierce@sltrib.com; follow him on Twitter @ScottDPierce. —