Spatial Data Format of the Week: GPX (GPS Exchange Format)

The Fitness Tracker's Native Language

File extension: .gpx

What it is: The standard XML-based format for GPS data, created specifically for exchanging routes, tracks, and waypoints between GPS devices and applications. If you've ever used Strava, Garmin Connect, AllTrails, or your smartphone's fitness app, you've created GPX files.

Born for Movement

GPX was designed around a simple question: "How do I share where I've been with someone else?"

Three Core GPX Data Types

1. Waypoints — Individual points of interest

<wpt lat="37.619" lon="-122.375">
  <name>San Francisco Airport</name>
  <ele>4.0</ele>
  <time>2024-01-15T08:30:00Z</time>
</wpt>

2. Tracks — Your actual path with timestamps (what you recorded)

<trk>
  <name>Morning Run - Golden Gate Park</name>
  <trkseg>
    <trkpt lat="37.7694" lon="-122.4862">
      <ele>15.2</ele>
      <time>2024-01-15T07:00:00Z</time>
    </trkpt>
    <trkpt lat="37.7695" lon="-122.4863">
      <ele>15.8</ele>
      <time>2024-01-15T07:00:05Z</time>
    </trkpt>
  </trkseg>
</trk>

3. Routes — Planned paths (what you intend to follow)

<rte>
  <name>Half Dome Trail</name>
  <rtept lat="37.7459" lon="-119.5332">
    <name>Trailhead</name>
  </rtept>
  <rtept lat="37.7459" lon="-119.5332">
    <name>Summit</name>
  </rtept>
</rte>

Common Data Sources

Fitness & Activity Tracking

Strava: Export individual activities or bulk download
Garmin Connect: Routes, activities, courses
AllTrails: Hiking trail recordings and planned routes
Komoot: Bike touring and adventure planning
Ride with GPS: Cycling routes and navigation

Smartphone Apps

iPhone Health/Fitness: Walking, running, cycling routes
Google Fit: Android activity tracking
Gaia GPS: Backcountry navigation and waypoint recording
Organic Maps: Offline hiking navigation

Handheld GPS Devices

Garmin, Magellan, TomTom devices
Dedicated hiking/marine GPS units
Survey-grade GNSS receivers

What Makes GPX Special

Temporal Tracking

Every trackpoint includes a timestamp, enabling:

Speed calculations: distance ÷ time between points
Elevation profiles: altitude changes over time
Activity duration and pace analysis
Temporal animations in GIS

Elevation Data

Includes vertical dimension (often from barometric altimeter or GPS):

<ele>1524.3</ele>  <!-- Elevation in meters -->

Rich Metadata

Beyond coordinates, GPX stores:

Activity type (running, cycling, hiking)
Heart rate, cadence, power (from sensors)
Description and notes
Creator software information

Analyzing GPX in QGIS

1. Import GPX File

Method A: Drag and Drop

Drag .gpx file into QGIS
Select layer type: tracks, routes, or track_points

Method B: Add Vector Layer

Layer → Add Layer → Add Vector Layer
Source: Select .gpx file
Choose sublayer (tracks, routes, waypoints)

2. Common Analyses

Calculate Total Distance:

# In Field Calculator
$length  # For line layers in layer CRS units

Calculate Average Speed (requires time field):

Convert track points to line
Add field: distance = $length
Calculate time difference between points
Speed = distance ÷ time

Elevation Gain:

Use Profile Tool plugin
Or sum positive elevation changes in track points

Create Activity Heatmap:

Collect multiple GPX files in one folder
Use Heatmap (Kernel Density Estimation) on track points
Style by activity frequency

Converting GPX for Analysis

To Shapefile/GeoJSON

Vector → GPS → GPS Tools
Or right-click layer → Export → Save Features As
Choose format (Shapefile, GeoJSON, GeoPackage)

From CSV to GPX

If you have lat/lon/time data in CSV:

Import CSV as delimited text layer
Use GPS Tools → Create GPX (if available)
Or export to KML, then convert to GPX online

Common Use Cases in GIS

1. Trail Mapping

Collect hiking trail data with smartphone
Import to QGIS for cartographic display
Overlay on satellite imagery for trail maintenance

2. Field Data Collection

Record sample site locations with GPS app
Add waypoints with photos and notes
Import to QGIS for spatial analysis

3. Activity Pattern Analysis

Analyze running routes for urban planning
Identify popular recreational corridors
Compare planned vs. actual routes

4. Volunteer Geographic Information (VGI)

Community trail mapping projects
OpenStreetMap contributions
Citizen science data collection

GPX Limitations for GIS

1. Not Designed for Analysis

Optimized for navigation and exchange
No spatial indexing
XML parsing overhead

2. Coordinate System

Always WGS 84 (EPSG:4326) latitude/longitude
No projection information needed (standardized)
May require reprojection for local analysis

3. Large File Sizes

XML text format is verbose
High-frequency GPS logging creates massive files
1-second interval track = 3,600 points per hour

4. Limited Attribute Structure

Designed for GPS-centric data
Not ideal for complex non-temporal attributes
Better formats exist for non-GPS field data

When to Use GPX

Best for:

Recording movement with GPS devices
Fitness and recreation tracking
Field data collection with smartphones
Sharing routes and waypoints
Temporal analysis with timestamps
Elevation profile analysis

Avoid when:

Static point data without temporal component
Large-scale spatial databases
Complex attribute relationships
Non-GPS spatial data
Performance-critical applications

Processing Tips

Simplify Dense Tracks

High-frequency GPS creates unnecessary detail:

Vector → Geometry Tools → Simplify
Use Douglas-Peucker algorithm
Tolerance: 0.0001° (≈10m) for most applications

Clean GPS Noise

GPS signal often includes erratic points:

Filter by speed (remove impossible velocities)
Remove elevation outliers (barometric noise)
Smooth tracks with moving average

Batch Process Multiple Files

Collect many GPX files:

Use Processing → Batch Processing
Apply same workflow to folder of GPX files
Merge results with Vector → Data Management Tools → Merge

The Bottom Line

GPX is the universal format for GPS data. If you're collecting spatial data in the field with consumer devices, you're creating GPX files. Learn to import, clean, and analyze them—they're the bridge between field work and desktop GIS.

Key takeaway: GPX files are "spatial data with timestamps"—perfect for anything that moves.

SDFotW - GPX & GPS Exchange Format