Rosetta Map, built by independent developer Riley Walz, uses GPT to translate neighborhoods between cities by finding their closest real-world analogs. Select a city you know well as your base and a city you want to explore as your target, and every neighborhood in the target city gets relabeled with its nearest equivalent from home. If you know New York and want to understand Tokyo, the map tells you which neighborhoods behave like the East Village or Tribeca — giving you an immediate foothold in unfamiliar territory.
The tool is more than a novelty. GPT first filters neighborhoods for general recognizability, then scores each one across five dimensions: density, cost, nightlife, transit access, and cultural significance. The model runs bidirectional matching between every city pair, generating a similarity score and a plain-language rationale for each proposed pairing. Rather than a greedy assignment approach, Walz applies the Hungarian algorithm — a classical combinatorial optimization technique for maximum-weight bipartite matching — to ensure the global assignment across all neighborhoods is jointly optimal. Street name analogs run through the same pipeline. The map renders with MapLibre on top of OpenStreetMap data.
Each match surfaces its rationale text, making the reasoning inspectable in a way that a pure algorithmic black box wouldn't allow. The Hungarian algorithm explanation is the strongest part of the design: it solves the real problem that greedy matching would leave you with a globally incoherent map, where one neighborhood hogs the best match and everything downstream degrades.
Rosetta Map has a direct predecessor in Walz's own Hopscotch.nyc, a neighborhood-matching tool limited to New York City built at Hack Lodge in 2022. The new version extends that idea globally and adds current-generation LLM scoring. Walz has built a string of high-concept solo projects — Bop Spotter, IMG_0001, Jmail — that share the same approach: a culturally legible problem, a technically rigorous solution, accessible to anyone.
The tool is live at walzr.com/rosetta-map.