What this is
One US map engine, any dataset as a layer. Add a dataset, stack as many as you want, click a city — the same rendering pipeline drives every one of Mapstack's 41 datasets, because every dataset implements one small, shared interface rather than getting its own hand-built map code.
It generalizes Allergy Locator, which shipped first as a real, validated US allergy-severity map. Once a second real dataset (healthcare access) got built the same way inside that project, the shared shape between the two became clear enough to actually generalize — rather than guessing at an abstraction from a single case.
Where the data comes from
Every dataset is real, free, and keyless — sourced from a public government agency (FBI, EPA, FEMA, CDC, USDA, Census, NOAA, BLS...) or a free public API, never scraped from behind a paywall or purchased from a data broker. When a source doesn't cover a city, or doesn't publish a field, that shows as a real, honest gap — never a fabricated value. See Sources for the full per-dataset list, or this repo's own data/*-methodology.md files for the real coverage numbers and known gaps behind each one.
Add to it, or just take it
This is open source (MIT licensed) — the whole point is that you don't need permission to use it. Adding a new dataset means implementing one small interface (getValue() returning a 0–100 concern score plus a one-line detail, per src/lib/datasets/types.ts), registering it once, and the exact same map, legend, detail panel, and year control all render it — zero new rendering code. Open a pull request, or fork the repo and run it entirely on your own:
- Source on GitHub — clone it, add a dataset, open an issue, or send a pull request.
- CONTRIBUTING.md — the step-by-step walkthrough for adding a new dataset.
- README — full setup, the dataset backlog, and every principle this project runs on.
- Zero required backend and $0 to run — it's a static Next.js build, so a fork deploys anywhere for free.
Support this project
Free and open source, always. A few ways to help — or just say hi:
- Use it, star it, file an issue. Honestly the best support an open-source project can get. → this project
- Hire me. I do fractional-CTO and consulting work — fixing and scaling tech stacks. → mdostal.com/contact
- Buy me a coffee if it saved you time.
- More tools like this → tools.mdostal.com
- Life outside the terminal → life.mdostal.com
- What we're building at Firefly Events — event discovery, 8,000+ events/day from 7+ sources → ff.events
Always up for a conversation if any of it's useful to you.
MIT licensed. Directional, not authoritative — every layer documents its own sourcing and limitations; nothing here replaces official records, professional advice, or your own research.