In New Horizons, what is the name of the app used to design your island?

In New Horizons, the app used to design your island is called Island Designer. It is a NookPhone application that unlocks the game's terraforming and path-building tools.

Island Designer becomes available after the player develops the deserted island far enough to receive a three-star island evaluation and host K.K. Slider's first concert. Once unlocked, it lets players place paths and, with additional permits, reshape cliffs and water. This turns the island from a fixed layout into a highly customizable landscape.

A common mix-up is calling the feature the NookPhone itself. The NookPhone is the in-game smartphone that holds several applications, including Island Designer, the Critterpedia, the map, and Nook Shopping. “Terraforming” describes what some Island Designer tools do, but it is not the app's official name. The app also does not let players enlarge the island or move its shoreline beyond the available map.