Developer Builds Digital San Francisco with 1,000+ AI Citizens and Live City Data

On August 21, developer David (@davidfromkansas) posted a series of updates on SFSIM, a 3D digital San Francisco hooked into live city data and populated by more than 1,000 synthetic citizens. He said he built it because he felt San Franciscans weren't online enough, and he plans to train and observe agents inside the simulation.

Confirmed

• The simulator ingests live feeds including Muni, BART, ferries, bike-share, traffic, weather, earthquakes and breaking news
• Over 1,000 synthetic citizens live daily lives and are active on a dedicated subreddit, r/simfrancisco
• The 3D city is procedurally generated with Three.js from public geospatial data, building footprints and crowdsourced information
• The building pipeline was built with Devin: given an address, it searches online via Exa to inform generation; it has produced roughly 170,000 buildings
• The simulator knows each building's real-world use (restaurant, commercial, residential), modeled on real public data

Why it matters

• David frames the project as a sandbox game-like environment for simulating the social intelligence of personified agents with human-like needs and goals
• He argues such simulations matter for scalable AI alignment: training agents to adopt beneficial behaviors and observing them in scenarios hard to replicate physically
• He notes the underlying techniques draw on a decade-plus of academic research, despite his non-PhD background, and that virtual environments can give agents spatial context for future training and observation
• The building pipeline (Devin + Exa + Three.js) is itself a reusable procedural city-generation workflow

2026-08-21 ~ 2026-08-21 · 6 related posts

• [source] Built a digital SF sim with 1,000+ synthetic citizens reacting to live city data — davidfromkansas · 2026-08-21
• He put San Francisco in a simulator: 1,000+ AI citizens live on their own subreddit — davidfromkansas · 2026-08-21
• [source] Devin + Blender pipeline generates 174,647 buildings for a simulated San Francisco — davidfromkansas · 2026-08-21
• 3D SF buildings grounded in real data; future plans to train agents with spatial context — davidfromkansas · 2026-08-21
• [source] Developer builds 3D virtual SF as training ground for AI agents, citing accessibility of techniques — davidfromkansas · 2026-08-21
• Why build a simulated SF? To train agents' social intelligence and alignment — davidfromkansas · 2026-08-21