Rust Wasm Geo

Rust / WASM geo

Default stack context: tech-stack skill. This skill covers Rust/WASM geo only.

When to apply

• Turf or JS geometry is too slow (profile first — main-thread blocking > ~100ms)
• OSM parsing, map model build, isochrones, spatial indexes, graph routing
• Thousands of features, repeated geometry ops, or polygon booleans at scale
• Adding or reviewing a wasm-pack crate, wasm.ts boundary, or Vite WASM plugins

Stay on Turf (JS) for single-feature ops on small GeoJSON and interactive editing feedback during prototyping.

Turf vs Rust/WASM

Batch geometry on large arrays (not routing/OSM): geoarrow-wasm instead of rolling your own.

Crate selection (quick)

Per-crate usage notes and WASM dependency versions: crates-and-packages.md.

Project structure

One crate per app, named for what it computes (geo-isochrone, route-buffer, …).

app/
├── wasm/
│   └── geo-isochrone/          # Rust crate (wasm-pack output → pkg/)
│       ├── Cargo.toml
│       └── src/
│           ├── lib.rs          # #[wasm_bindgen] surface only
│           └── isochrone.rs    # pure geo logic
└── src/
    └── features/isochrone/
        ├── wasm.ts             # sole JS import of pkg — React never imports pkg directly
        └── useIsochrone.ts     # React hook / Query wrapper

• lib.rs = #[wasm_bindgen] exports; inner modules = pure geo logic (testable without WASM).
• JS boundary: wrap exports in wasm.ts. Pass GeoJSON strings or bincode Uint8Array — not hand-built JS objects.
• State split: durable compute state in Rust; UI state in React (Zustand / URL / local useState).

WASM stack (Cargo)

Build: wasm-pack (--target web), vite-plugin-wasm, target wasm32-unknown-unknown.

Reference setups: a-b-street/ltn, a-b-street/15m, a-b-street/utils.

Docs when stuck: wasm-bindgen book, geo on docs.rs.

App integration

Both: dynamic-import WASM from wasm.ts only; never top-level import of .wasm in shared modules that may load on the server.

Non-negotiable rules

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