Most navigation apps need a connection to know the speed limit. ZMap does it differently: a per-road speed-limit database is built from OpenStreetMap data and lives on the server. When a route is computed, each trip point is snapped to the nearest road and given its speed. The full route — speeds included — is then cached on the phone: while driving, no network request is needed.
highway).
osmium tags-filter keeps
only the roads (8.5 GB), then only those carrying a speed
(maxspeed) are kept — about 13 million.
It is fully reproducible: the build script
(build_maxspeed.py) runs end to end on a small server.
Share of points by speed limit (most common values) :
| Limit | Share | |
|---|---|---|
| 50 km/h | 26.2% | |
| 30 km/h (30 zones) | 18.5% | |
| 90 km/h | 9.5% | |
| 80 km/h | 9.2% | |
| 70 km/h | 6.0% | |
| 60 km/h | 5.7% | |
| 100 km/h | 4.6% | |
| 40 km/h | 3.3% | |
| 48 km/h (30 mph, UK) | 2.8% | |
| 97 km/h (60 mph, UK) | 2.4% | |
| 32 km/h (20 mph, UK) | 2.1% | |
| 20 km/h (pedestrian zones) | 2.1% | |
| 120 km/h | 1.8% | |
| 130 km/h (motorways) | 1.7% | |
| 110 km/h | 1.4% |
Numeric values found in OpenStreetMap. Actual limits may
differ (roadworks, temporary signs, weather). Roads with no limit
(e.g. some German sections) have no maxspeed: ZMap then
shows no speed.
The server returns, with every route, an array of speeds aligned with the geometry points (one value per point). The phone stores everything in its local cache: while driving, the current section's limit is read without network, and offline mode keeps the whole trip. Snapping a 4,500-point route takes about 170 ms on the server.