What GPS Records Can and Cannot Prove in Litigation

Attorneys frequently encounter GPS evidence in civil and criminal litigation under the assumption that it functions like an infallible digital breadcrumb trail. Whether extracted from a defendant’s smartphone, a commercial trucking fleet GPS tracker, a Lyft or Uber rideshare app, a Garmin fitness device, or a court-ordered ankle monitor, latitude and longitude coordinates carry an aura of mathematical certainty.

In court, opposing counsel may plot a series of raw coordinates in Google Maps and declare the matter settled: that the driver was speeding, the defendant was at the crime scene, or the vehicle made an unexplained stop. For a forensic engineer, raw coordinates are only the beginning of the inquiry. GPS is a radio frequency (RF) based satellite trilateration technology subject to environmental conditions, physical constraints, signal degradation, software filtering, and hardware limitations. Knowing what GPS data proves, and where an opponent’s reading fails under technical scrutiny, can change the trajectory of a case before trial even begins.

What GPS Records Can Reliably Establish

When preserved correctly and analyzed with a strong understanding of the science and engineering disciplines that make GPS possible, GPS data provides robust, defensible evidence on several core questions.

General Route Trajectory and Temporal Sequences

Under ideal conditions, consumer and commercial GPS receivers can provide reliable location estimates. Comparing adjacent data points over time can demonstrate whether a vehicle was traveling along a known corridor, when a trip commenced, where directional changes took place, and the chronological sequence of events relative to third-party records such as call detail records, dispatch timestamps, or surveillance video.

Sustained Stops vs. Motion

A vehicle or person remaining stationary for an extended period leaves a recognizable data signature. While the position might jitter slightly due to receiver drift, the clustering of points combined with speed validation can confirm that a device was stationary at a specific facility, address, or intersection.

Calculated Average Velocity

When speed data is absent from logs, an engineer can compute ground speed between adjacent points using the Haversine formula and the fundamental time-distance kinematic equations. When corroborated across several consecutive intervals, this calculation provides a mathematically sound average speed over a roadway segment.

Where GPS Evidence Often Breaks Down

Litigators encounter serious problems when raw coordinates are taken at face value without accounting for satellite geometry and spacing, environmental conditions such as tall buildings, bridges, and other sources of reflection, and platform-specific quirks.

Multipath Interference

GPS receivers calculate distance by timing how long a radio signal takes to travel from GPS satellites to the receiver antenna. In urban environments, mountainous terrain, or industrial parks, the same satellite signal can reach the receiver via multiple paths. A satellite signal may reach the receiver along a direct path, and that same signal can also bounce or reflect off the road, buildings, bridges, concrete structures, or rock faces before reaching the receiver. When the receiver picks up both the direct and reflected signals, multipath interference can occur, resulting in errors in the reported latitude and longitude coordinates.

Obstructions, Reflections, and Urban Canyons

GPS location errors can also result when direct signals are blocked by obstructions such as buildings, trees, mountains, or bridges. In this scenario, the strongest signal comes from a reflection off a building, the road, or some other structure. The reflected signal travels a farther distance than the direct signal would have, and that extra distance produces location errors. The recorded location may appear blocks away on a nearby road or alley, or even show a vehicle driving through buildings and over sidewalks. The location can also appear to jump around randomly.

GPS “Drift” While Stationary

Another common misinterpretation in criminal matters and rideshare litigation is mistaking GPS drift for physical motion. When a phone or ankle monitor sits motionless indoors or under partial cover, the receiver continually attempts to lock onto weak satellite signals. As satellites orbit the earth and atmospheric conditions shift, the calculated coordinates can wander or drift around the actual location. An untrained observer looking at the record might argue that a suspect walked down a street or circled a vehicle when the device actually sat motionless for an extended period of time.

Dilution of Precision (DOP) and Satellite Constellation Geometry

A GPS receiver needs a fix on at least three to four satellites to determine its location. When the satellites are spread out across the sky, precision is high and the position estimate is reliable. When the satellites are grouped together in one quadrant of the sky, precision is low and the position estimate may be unreliable. A coordinate fix that looks precise on a map may actually represent a large uncertainty.

Variable Polling and Interpolated Logs

Some apps and fleet software do not continuously record position. To conserve battery or network bandwidth, or for other reasons, GPS coordinates may be polled or recorded only every 30, 60, or 120 seconds. Some systems only poll and record coordinates when there is a change in acceleration, such as speeding up, slowing down, or changing direction. A proprietary post-processing algorithm is then used to fill in the missing data and estimate the vehicle’s location. Don’t assume that records produced through variable polling and proprietary algorithms are accurate.

Gaps in the GPS Record

Not all GPS logs contain a continuous record of someone’s position in space and time. Gaps in a GPS record must be systematically identified and assessed. Gaps in time could indicate variable polling, a processing error, or that the app or GPS receiver was turned off. Gaps in location can also indicate that the receiver was turned off, or they can point to a weak signal environment that calls the validity of the data into question.

The Litigator’s Checklist: Evaluating GPS Evidence

When subpoenaing, inspecting, or challenging GPS records, counsel should insist on technical transparency.

Evidentiary Requirement	Why It Matters Technically
Raw GPS Logs	Raw logs containing latitude, longitude, and timestamp are a minimum requirement. When additional metadata are available, such as satellite count, DOP, and signal-to-noise ratio (SNR), these should be produced as well.
Continuous Records	Unexplained gaps in a GPS record can raise questions about the validity of the record in space and time.
Device Source Identification	A hardwired GPS system with an external roof antenna has different capabilities than a smartphone. Different smartphone models also have different capabilities.
Time Standards (UTC vs. Local) and Date	Timestamps can be recorded in different standards. Without the time standard and date, conversions to the desired time zone cannot be determined.

Bridging the Gap for Judges and Juries

Presenting GPS data in deposition, mediation, or trial requires transforming raw coordinate files into clear, objective exhibits that withstand scrutiny under Daubert or Frye standards.

• Independent Coordinate Audit: Verifying that distance, elapsed time, and implied physics such as acceleration and braking rates conform to real-world dynamics.
• Uncertainty Assessment: Showing and explaining the uncertainty and margin of error so the judge or jury can assign the proper weight to the evidence.
• Correlating Disparate Data Streams: Cross-referencing GPS logs against call detail records (CDRs), cell site sector azimuths, Wi-Fi BSSID handshakes, GPS logs from other sources, and physical evidence to form a single, coherent timeline.

Why Litigators Need to Retain an Engineer

GPS is built upon decades of advancements in science and engineering. You need an expert with the right knowledge, skill, training, and experience in the disciplines that make GPS possible: RF propagation, wireless communications, receiver design, signal processing, and the physical sciences. It’s imperative for your case that you retain a licensed and experienced engineer to review your GPS records.

Discovery Engineering (Mark McFarland, P.E.) provides forensic electrical and telecommunications engineering, expert witness testimony, report preparation, and objective cellular and GPS data analysis nationwide in matters involving GPS records, cellular tracking, and electrical and electronic evidence. If your case turns on location data, discuss a case with Mark directly.