GPS and Telematics Terms, Explained Without the Sales Deck
Telematics vocabulary is borrowed from satellite navigation, automotive electronics and mobile networks, and vendors rarely stop to define it. This sheet covers the terms you will meet in a specification, a support ticket, or an argument about why a vehicle appeared in a field.
Somebody calls to say the tracker is broken. The van is showing in the middle of a car park it has never visited, one street from where the driver says he is. He is probably right, and so is the device: it is parked between two tall buildings, and the signal it used to fix its position bounced off one of them before it arrived.
Almost every telematics dispute is like this. Not a fault, but a limit of the technology that nobody explained, dressed up as a fault. The vocabulary matters because it is the difference between raising a support ticket and understanding your own data.
The last group on this sheet is the one worth reading twice. It covers accuracy — the terms that describe what satellite positioning cannot do. A vendor who volunteers those before you buy is telling you something useful about how the rest of the relationship will go.
Positioning and satellites
| Term | What it means |
|---|---|
| GNSS | The umbrella term for satellite positioning systems. Almost everything sold as GPS today is really GNSS, using several constellations at once. |
| GPS, GLONASS, Galileo, BeiDou | The four main constellations, run by the United States, Russia, the European Union and China. A receiver using more than one fixes faster and holds position better in cities. |
| Fix | A calculated position. It needs signals from at least four satellites: three for position and one to resolve the receiver's own clock error. |
| HDOP | Horizontal dilution of precision. It describes satellite geometry rather than signal strength, so satellites bunched in one part of the sky give a poor fix even at full signal. |
| TTFF | Time to first fix. How long from powering up to a usable position, which is why the first hundred metres of a trip are often missing. |
| Cold, warm and hot start | How much the receiver remembers. A hot start has current satellite data and fixes in seconds; a cold start knows nothing and can take minutes. |
| A-GPS | Assisted GPS. The device downloads satellite orbit data over the mobile network instead of waiting to hear it from the satellites, cutting time to first fix. |
| Dead reckoning | Estimating position from last known fix, heading and speed when satellites are unavailable. It keeps a vehicle plausible through a tunnel and accumulates error the whole way. |
| Multipath | A signal that reached the receiver after bouncing off a building. It arrives late, the receiver reads late as far away, and the vehicle jumps a street sideways. |
Devices and connectivity
| Term | What it means |
|---|---|
| Diagnostic port tracker | A unit that plugs into the standard socket on a light vehicle. It installs in seconds and can be unplugged just as fast, which is the whole trade-off. |
| Hardwired tracker | A unit wired to permanent power, ignition and often the vehicle bus. Harder to fit, and considerably harder to remove quietly. |
| CAN bus | The internal network the vehicle's modules talk on. Reading it is how a tracker knows fuel level, engine hours and fault codes rather than guessing from movement. |
| J1939 | The heavy-vehicle standard riding on CAN. It defines parameters and their failure modes, which is why truck data is richer than light-commercial data. |
| Ignition sense | The wire or signal telling the device the engine is running. Trips, idling, engine hours and fuel logic all depend on it being right. |
| Asset tracker | A battery-powered unit for trailers, plant and containers, reporting a few times a day. It answers where, not how, and lasts years by not trying to answer more. |
| IMEI | The unique hardware identifier of the device's cellular modem. It is the number your provider will ask for before anything else. |
| M2M SIM | A machine-to-machine SIM on a data-only plan, usually roaming across networks so the device attaches to whichever one has coverage. |
| LTE-M and NB-IoT | Low-power cellular standards built for devices rather than phones. Longer battery life and better building penetration, at data rates that would be useless for anything else. |
| Store and forward | The device buffers readings when it has no signal and uploads them when coverage returns. It is why a rural trip fills itself in retrospectively rather than staying blank. |
| OTA update | Firmware pushed over the air. Its absence means a fleet-wide bug is fixed by visiting every vehicle, which is a cost nobody quotes for. |
Platform concepts
| Term | What it means |
|---|---|
| Breadcrumb trail | The sequence of position reports that makes up a trip. Its usefulness is set entirely by reporting interval — sixty seconds turns a roundabout into a straight line. |
| Reporting interval | How often the device sends a position. Frequent reporting costs data and battery and buys detail, and the right answer differs for a trailer and a delivery van. |
| Geofence | A virtual boundary around a place. Entry and exit generate events, which is how arrival times stop depending on a driver remembering to call in. |
| Point of interest | A named location on the map: depot, customer site, fuel station. Without it every report reads as raw coordinates and nobody can scan it. |
| Trip | The platform's unit of work, usually bounded by ignition on and ignition off. Every per-trip figure you report inherits whatever that definition got wrong. |
| Idling | Engine running, vehicle stationary, beyond a threshold you choose. The threshold is the argument: too short and every traffic light counts, too long and nothing does. |
| Harsh event | Acceleration, braking or cornering beyond a set force. Meaningful only against a fixed threshold, since lowering it improves any driver's score overnight. |
| Snap to road | Correcting a reported position to the nearest plausible road. It makes maps readable and quietly hides the fact that the raw fix was thirty metres out. |
| Trip replay | Playing a recorded journey back with its speed, stops and sensor data. It is what turns a customer dispute from two accounts into one record. |
| Driver ID | A tag, fob or app login that attaches a person to a vehicle. Without it, everything you measure belongs to a registration plate rather than to anyone. |
| Webhook | A push from the platform to your system when something happens, rather than your system asking repeatedly whether anything has. The difference between integration and polling. |
Accuracy and its limits
| Term | What it means |
|---|---|
| Urban canyon | Streets narrow enough that buildings block most of the sky and reflect the rest. Position error grows exactly where drops are densest and disputes are most likely. |
| GPS drift | A stationary vehicle whose reported position wanders. Harmless on a map, and it silently adds distance to any odometer built by summing positions. |
| Jamming | A transmitter drowning out satellite signal, usually from a cheap device in a cab. The symptom is not a wrong position, it is no position, on one vehicle, repeatedly. |
| Spoofing | Fake satellite signals producing a confident and wrong fix. Rare, and worth knowing about because it is the one failure that looks entirely normal on screen. |
| Coverage gap | The device has a position but no network to send it on. Buffering closes most of these, which means the data was true when recorded and late when it arrived. |
| Latency | The delay between something happening and you seeing it. A live map is always a report of the recent past, and the honest question is how recent. |
| GPS versus odometer distance | Two different numbers that will never agree. GPS sums straight lines between fixes and under-reports bends; the odometer counts wheel rotations and moves with tyre wear. |
Frequently asked questions
Good enough to know which road, usually not good enough to know which lane, and worse than the specification sheet implies. Open motorway with clear sky is the best case. A yard surrounded by warehouses, a city centre, or a vehicle parked under a canopy is the worst, and error there is measured in tens of metres. The figure vendors quote is a best case under ideal conditions, and your fleet does not work under ideal conditions.
Because they measure different things and neither is lying. Satellite distance is the sum of straight lines drawn between position reports, so every curve between two fixes is cut short and a sparse reporting interval loses more of it. The odometer counts wheel rotations, which changes as tyres wear and differs again between tyre sizes. Expect a small persistent gap. Pick one source for any given report, say which it is, and stop reconciling them.
Some can, and it is better to know how. A plug-in diagnostic-port device can be unplugged. A cheap jammer in a cigarette lighter socket will stop a unit reporting. Foil over an aerial degrades a fix. What none of those achieve is silence: a device that stops reporting raises a health alert, and a vehicle going dark on the same shift every week is a pattern that surfaces faster than the driver expects. The defence is not an untamperable device. It is treating absence of data as information.
It depends on what the data decides. Answering where a driver is while a customer waits on the phone needs current position. Costing a route, auditing hours, or proving a delivery happened needs an accurate record rather than a live one. Frequent reporting costs data and battery, and on an asset tracker it costs years of field life. Most fleets buy a reporting rate for a use case they never actually have. Ask what decision changes if the report is ten minutes old.
Almost anything, so ask three specific questions. Can you export raw position and sensor data, or only the reports their platform chooses to render. Can you receive events as they happen, or must you poll for them. And is your history available after the contract ends, in a format that is not a screenshot. A readable API is table stakes; the thing to settle before signing is whether the data you are about to accumulate belongs to you.
See these metrics on your own fleet
GPS Fleet Tracking Software reports every one of these numbers from live operational data.