Speed and speed limit

What does MoveJack do?

During a trip, the home screen shows your speed next to a traffic sign with the limit in force. If no limit is known, it shows a dash.

For each GPS point, the app stores on your phone which limit applied at that moment. It uses that for the speed graph in the trip details and for the trip score.

How does it work?

The app sends the position at that moment to Overpass, a public search service for OpenStreetMap map data, through one of four fixed servers. The question is: which roads with a speed limit lie within 20 meters? The app takes the limit of the nearest road. The app uses no other source.

The app stores limits it has found on your phone, per square of about 11 by 11 meters. When you pass such a square again, no new request goes out.

How often does a position go to the map service?

At most once every 8 seconds, and never two requests at the same time. While driving, that comes down to about one position every 8 seconds, except on stretches of road whose limit is already stored on your phone.

The app does this for every location point it processes, so not only during a trip. It happens as long as the app itself is running, in the background too. Outside a trip the app keeps the limit up to date this way: it passes it on to the next location points, so that they already have a limit when they become part of a trip.

The request contains a position, without a name or account. It states that it comes from the MoveJack app, not from whom. Together, though, those requests show your route, and as with any internet connection the service sees the IP address of your connection.

Filling in missing limits

If you open a trip with missing limits and you have internet, the app fills them in with a sample of route points. Places whose limit is already stored on your phone do not go to the service again.

If that fails, for example without a connection, the app tries again when you open the trip again.

If there is no limit

If the service returns no limit, the app keeps the previous one. If no limit was ever found, the dash stays. The app converts a limit in miles per hour into kilometers per hour.