Rated areas
Polygons
Each has a name, a city, a rating for each of the three time bands, crime types and a source. Soft-deleted, never hard-deleted, so history can be recovered.
red · orange · yellow · none
Under the hood.
Tsamaya is a React Native app backed by a geospatial database and a Python data pipeline with a Claude-assisted review step. Here is how the pieces fit.
The stack
Proven tools, boring in a good way
- React Native and Expo
- Cross-platform app, New Architecture enabled. Expo Router for navigation, EAS for builds and over-the-air updates.
- Mapbox
- Map tiles, the Directions API for routing, and Geocoding for naming the place you tap on the map. Search itself runs on Google Places.
- Supabase and PostGIS
- Postgres with PostGIS geometry holds every rated area and road. The app reads it live; the editor writes through typed RPC functions.
- Python data pipeline
- Map data fetched, scored for crime density, classified into rated areas and roads, staged, then promoted to live.
- Claude review
- An AI second opinion on the ratings, researched against local reporting. A person then sense-checks the results and looks closely at any rating that stands out.
- GitHub and EAS
- Versioned SQL migrations keep the database reproducible; TestFlight and Google Play open testing get builds to testers.
Three repos, one system
How data becomes a route
Crime and map data flow through a pipeline, get reviewed, then go live for the app to read.
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01 · Sources
OpenStreetMap, published SAPS crime statistics, drivers' reports
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02 · Pipeline
Fetch, score for density, classify areas and roads, stage
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03 · Review
A Claude second opinion, then a person sense-checks what stands out
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04 · Live database
Rated areas and roads in Supabase (PostGIS)
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05 · App
Tsamaya reads it live and plans the route
The routing model
How a detour gets decided
A small set of deliberate rules, tuned over real South African routes, that decide when a detour is worth it and when it is not.
- What triggers a detour
- Only higher-risk areas. Caution-level areas are drawn on the map but never trigger a detour.
- Route check
- The route is sampled and tested against every active area for the current time.
- Checked roads
- Recognises when a route already runs along a road we have checked, and leaves it be.
- Detour limits
- Bypasses are capped so they never wander unreasonably far from the direct line.
- Choosing a way round
- Only nearby checked roads are used to steer around a high-risk area.
- Sanity check
- Any detour that ends up excessively longer than the direct route is rejected. You get the direct route, clearly flagged.
- Time-aware
- Separate ratings for daytime, evening and night.
Data model
Rated areas and roads
Rated roads
Line strings
Each has a buffer width and marks a road as checked (preferred when threading past risk), flagged (avoided where there is a sensible way round) or closed (gated or impassable, so routed around without being counted as risk). The stored values are safe, danger and blocked: a checked road is one we have reviewed, not a promise about it. Identity is always (city, name), because road names repeat across metros.
checked · flagged · closed
Geometry is stored as PostGIS geometry and written through ST_SetSRID(ST_GeomFromGeoJSON(...), 4326) RPCs, since PostgREST cannot cast GeoJSON to geometry by itself.
Coverage
Where Tsamaya works today
Live across Gauteng (Johannesburg, Pretoria, Ekurhuleni and the West Rand), Durban, Pietermaritzburg, Gqeberha, East London, Port Alfred, Mthatha, Cape Town and Stellenbosch, Rustenburg and Pilanesberg, Mossel Bay and George, Beaufort West, Secunda, eMalahleni and Middelburg, Bloemfontein with Botshabelo and Thaba Nchu, Polokwane, and Kruger National Park with Mbombela and the Lowveld. Adding a city follows a documented runbook, which is how the map went from one city to 22 places.
22 Places mapped
6 649 Rated areas
2 931 Checked road stretches
3 Time bands
Talk shop
Curious, or want to help build it?
We are always glad to talk shop, or to find sponsors who want to fund the next metro.