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Three different things travel under the name “GPS”. The satellite signal tells a device where it is. The map tells it what surrounds that position. The software turns the two into directions. Of the three, only the satellite signal stays current by itself; the map and the software change only when a maker publishes a new release and that release reaches the device.
What a map release holds
A map release is less a picture than a database. A dashboard navigator draws its screen from that database and calculates every route through it, so each layer below affects what the driver sees and where the device sends the car.
| Layer | What it holds | What drifts as it ages |
|---|---|---|
| Terrain and water | Coastlines, rivers, lakes, parks and the shape of the land. | Rarely much; this layer changes slowly. |
| Road network | Every road’s geometry and connections, one-way rules, turn restrictions, tolls and ferries. | New roads, roundabouts, closures, re-routed junctions. |
| Addresses and names | Street names, house-number ranges and postal codes. | New streets and developments that the device cannot find. |
| Places | Businesses and services, often called points of interest: fuel, food, lodging, hospitals. | Openings, closures, moves and renamed brands. |
| Speed limits and lanes | Posted limits, lane counts and, on some devices, junction drawings. | Changed limits announced wrongly or not at all. |
| Vehicle restrictions | On truck and RV products: clearances, weight limits, restricted roads. | New low bridges, re-rated structures, new bans. |
How quickly the ground changes
Road networks change constantly and quietly. A housing estate adds a dozen streets; a junction becomes a roundabout; an exit is renumbered; a bypass opens and the old route through town is downgraded. Each change is small, but a navigator’s map collects every one of them as a difference from reality.
The effects show up in predictable ways. A device with an older map plans around a road it has never heard of, cannot find an address on a street built after its release, sends a driver to a restaurant that closed, or announces a speed limit that has since changed. None of this means the device is faulty: it is doing exactly what its map tells it to do.
Where map data comes from
Some makers of navigators also build map data; others license it. TomTom is both a navigator maker and a map maker. Garmin’s lifetime map terms refer to map data that Garmin receives from a third-party supplier. HERE supplies the map data in a great many factory car systems, while the carmakers decide how those systems receive it.
Drivers contribute too. TomTom’s Map Share, for instance, passes corrections made by its users — a changed speed limit, a new turn restriction — to other TomTom devices between full releases.
Releases and their labels
Makers publish maps on a cadence rather than continuously. Garmin’s manuals describe its LM models as receiving quarterly releases, and its nüMaps Lifetime terms speak of up to four a year. Each release carries a version label, commonly built from a year and a sequence number, and the maker’s own software compares the label on the device with the newest one published for that model.
Why every release is larger
Every release tends to be bigger than the one before. Coverage widens, roads gain detail, lane and junction data are added, and the number of places grows. By TomTom’s own account in 2018, its European map was roughly four times the size it had been three years earlier: 6.5 GB, up from 1.6 GB.
A navigator’s storage, by contrast, is fixed on the day it is made. Sooner or later a current map no longer fits, and at that point the maker stops publishing releases for the model. The guide on lifetime terms follows that story to its end.
What an old map gets wrong, and what it does not
An aging map does not touch positioning. The satellites keep giving an accurate location, and the device keeps drawing that location on its last map. What goes wrong is everything the map is supposed to know about the ground around that position.
- Routes can avoid a fast new road and use a slower old one.
- An address search can fail for a street built after the release.
- Speed limit warnings can be out of date in either direction.
- Places in the device’s directory can be closed, moved or renamed.
Each of these comes from the map’s age, and each disappears only with a newer release published by the maker.