For a long time, what is, and what is not, Paris was defined by the 21-mile beltway that encircles it. Inside the Périphérique, as the road is known, was the romantic city of gilded bridges and ageless beauty that inspired the most famous line in the movies, Humphrey Bogart’s epitaph for love: “We’ll always have Paris.”

Beyond it, in the banlieue, or suburbs, home to many immigrants, stood dilapidated public housing. From time to time, as in 2005, riots erupted. The postal code 93, denoting the vast department of Seine-Saint-Denis north of the city, was synonymous to some with troubled dereliction, however reductive that stereotype became over time.

Forget all that. Greater Paris is born, reconfiguring the city. The Périph, a moat no longer, has steadily become porous. The east, long snubbed by the bourgeoisie of western Paris, has risen, turning the banlieue from Pantin to Romainville into cool, desirable areas. Tourists troop to the Louvre, but the action is no longer on the Seine River — it is on a 200-year-old canal, the Ourcq.

“In Pantin, I always feel I’m in the future, and in central Paris, I’m stuck in the past,” said Rémi Babinet, the founding chairman of the BETC advertising agency, which moved its headquarters from the city to Pantin in 2016. “Tourists pay a lot to see a Paris that never moves, but they are going to have to discover a different one that does.”

Mr. Babinet’s offices look out over the gently flowing waters of the Ourcq (pronounced “Ork”), which began life bringing drinking water to Paris and, not so long ago, flowed past a squalid industrial zone of factories for cigarettes, steel boiler tubes, toilets and mopeds.

“Stolen cars got dumped in the water,” said Laurence Lavillière, recalling her childhood. She was born in 1972 and has lived her entire life in Pantin. “The canal was a no man’s land of drugs and garbage.”