Rumor has it that when South Korean director Bong Joon Ho decided to adapt the graphic novel La Transperceneige, what attracted him most wasn't the potential for action or the text's overarching social commentary, but the setting. Snowpiercer takes place entirely on a transcontinental train. From car to car, tail to engine, we find society represented in miniature; the remaining population of a now frozen Earth bound to an extreme class structure. They circle the globe once a year, never disembarking. At the head, the engine's godlike creator shrouds himself in mystery. He's built an arc, and on it collected a traveling show of civilization's political nightmares.
In his wake, each car plays a role in an intricate, life-supporting system. The wealthy ride towards the front with their clubs, spas, and gardens. The unlucky bring up the rear, packed like sardines into a rolling tenement. Here they feed on gelatinous protein bars, bound together by circumstance as they're mercilessly controlled, counted, and picked off without reason. Many of them have missing limbs, some have been separated from their children, all are caked in dirt and on the verge of revolution.
The improbability of the self-sustaining engine is part of Snowpiercer's beauty, and one Bong Joon Ho clearly understands as a type of character; a true mechanical god for the characters on board. The fact of the train, of the constant forward momentum, the things it contains, the spaces it opens up and decisions it necessitates, are what makes the film a truly special work of dystopian science fiction. Rules matter more than they might in open spaces. Continuity matters, progress matters, and world-building becomes inseparable from the story.