Every carrier publishes a map of where it says it has coverage. LastBar's map shows where phones actually had signal. Both are useful, and they are not the same thing.
Predicted, or measured
A carrier's coverage map is, for the most part, a prediction. It is worked out by software from where the towers are, how strongly they transmit and the shape of the land, and it shows where the signal should reach. Such models can be wrong in the places that matter most to someone outdoors: deep valleys, the far side of a ridge, the edge of the network. In 2019 the Federal Communications Commission of the United States drove nearly 10,000 miles testing the maps of three carriers there, and found that its tests reached the minimum speed the maps predicted only 62.3% of the time.
LastBar's map is measured. Every coloured hexagon is a place where a phone with LastBar was, and what it found there: excellent, good, fair, weak or no signal at all. Where nobody has been yet, the map is empty, and says so.
In short
| A carrier's coverage map | LastBar | |
|---|---|---|
| Where it comes from | A model of the network, made by the carrier | Readings of phones that were there |
| Carriers | Its own | All of them, or the one you pick |
| Where nobody has been | Filled in by the model | Empty, or the estimated position of towers, marked as an estimate |
| Places with no signal | Shown as gaps in the prediction | Shown where phones measured none |
| Works offline | Usually a web page | Yes, on your phone |
| Guides you to signal | No | Find Signal: distance and direction to the nearest signal |
How to use both
- Choosing a carrier for a farm or a holiday house: read the carrier maps, then look at LastBar to see what phones found there, carrier by carrier.
- Before a trip: save the area in LastBar, so you have the measured map with no connection.
- In an emergency: an emergency call goes through on any network your phone can reach, not only your own. LastBar's Find Signal looks at every carrier for that.
The figures of the FCC are from its staff report on the coverage maps of three carriers in the United States, of December 2019. LastBar names no carrier here: the point holds for any network's predicted map.
