GPX glossary: files, measurements, maps and hiking
The words that come up when you open, convert or plan a GPS track, each defined in one to three sentences. The calculation figures are those of the site’s tools and the Mac app, detailed on the About page.
56 terms
Files and formats
GPX (GPS Exchange Format) is an open XML file format, published by TopoGrafix, for exchanging GPS data between devices and software. Version 1.1, from 2004, is the one in common use. A file can hold tracks, routes and waypoints.
On the site: Open a GPX file online
A track is an ordered list of points describing a path (the trk element). It is what a watch or a phone records during an outing, or what you draw on a map. It is split into one or more segments.
A route is an ordered list of waypoints to reach one after the other on the way to a destination (the rte element). It has few points: the GPS device works out the path between them, whereas a track fixes the whole line.
On the site: GPX Path for Mac exports either as a track or as a route.
A segment (the trkseg element) groups track points that are connected in order. The GPX specification asks for a new segment at each break, for instance when GPS reception is lost or the device is switched off, so a track can have several segments.
A track point (the trkpt element) carries a latitude and a longitude in decimal degrees (WGS84), and often an elevation in metres and a time. A track’s distance and elevation gain are worked out from point to point.
A waypoint (the wpt element) is a single named point: a summit, a spring, a mountain hut, a car park. The GPX specification describes it as a waypoint, point of interest or named feature on a map; it is not part of the line.
On the site: The GPX viewer shows waypoints as white dots, with their name on hover.
The metadata section of a GPX file describes the file itself: name, description, author, copyright, date, keywords and geographic bounds. It is optional.
The extensions element lets a GPX file carry elements from another XML schema. Manufacturers use it for data the format does not cover, such as heart rate or cadence.
KML (Keyhole Markup Language) is an XML format for showing geographic data on a map or a globe, born with Google Earth and an OGC standard since 2008. It describes lines, placemarks and polygons with their styles; point times only appear in gx:Track paths.
On the site: Convert: KML to GPX, GPX to KML.
A KMZ is a ZIP archive holding a main KML file and, sometimes, supporting files such as icons or images. It is stored and shared as a single file.
On the site: Convert a KMZ to GPX
FIT (Flexible and Interoperable Data Transfer) is Garmin’s binary format for data from sports watches, bike computers and sensors. It is compact and stores the activity with the track, heart rate or cadence; it is read by software, not in a text editor.
On the site: View a FIT file and convert it to GPX
TCX (Training Center XML) is a Garmin XML format that came with its Training Center software. It describes an activity split into laps, with heart rate, cadence and calories, where GPX describes a series of points.
On the site: The GPX converter reads TCX files.
GeoJSON is a JSON-based format for geographic data, standardised by the IETF in 2016 (RFC 7946). Coordinates are in WGS84 and are written longitude first, then latitude, the reverse of the usual order.
A timestamp is the time recorded with each point (the time element). In a GPX file it is in Coordinated Universal Time (UTC), in ISO 8601 format, not local time. It is what duration and speed are worked out from.
On the site: For a timestamped file, the viewer shows the time between the first and the last point, breaks included.
A GPS receiver gives an estimate of its position, not its exact position. Under open sky, a smartphone is typically accurate to within 4.9 m, according to the official US GPS site (gps.gov); the error grows near buildings, bridges and under trees. These small errors inflate elevation gain unless elevations are smoothed.
Simplifying a track means removing points without distorting the line too much, to make the file lighter or to suit a device that limits the number of points. The Douglas-Peucker algorithm, used by GPX Path, keeps the points that stray by more than a given tolerance in metres.
On the site: GPX Path for Mac offers simplification on export.
Measurements
A track’s distance adds up the gaps between its successive points. GPX Path measures them on a sphere with a 6,371 km radius (the haversine formula), without counting the slope: it is the flat distance, as on a map.
On the site: How the numbers are calculated
Elevation gain, written D+ in French, is the sum of all the climbs on a route, in metres. It often exceeds the gap between the lowest and highest points: a ridge that goes up and down counts every climb. GPX Path works it out from elevations smoothed over 100 m, with a 5 m threshold.
On the site: How elevation gain is calculated
Elevation loss, written D- in French, is the sum of all the descents on a route, in metres. GPX Path works it out with the same smoothing and threshold as elevation gain.
These are the lowest and highest points on the route. GPX Path reads them from the smoothed elevations, so they can differ by a few metres from a summit’s height on the map.
On the site: The viewer shows them under the map.
Smoothing replaces each point’s elevation with the average of nearby elevations, to remove the small variations caused by GPS or by the terrain model. GPX Path averages over 100 m of track, like the Mac app; without smoothing, a recorded track’s elevation gain is inflated.
On the site: How the numbers are calculated
After smoothing, a climb or a descent only counts once it exceeds a threshold: 5 m in GPX Path. Smaller ups and downs are ignored. Other tools use other settings, hence a few per cent of difference with Garmin Connect or Strava.
On the site: How elevation gain is calculated
Grade is the ratio of elevation change to flat distance, as a percentage: 10% means 10 m of climb for every 100 m travelled. A 100% grade is a 45° slope.
On the site: GPX Path for Mac can show a slope map as an overlay.
An elevation profile is the chart of elevation against distance travelled. It shows where the climbs are, how long and how steep.
On the site: In the viewer, hovering over the profile shows the matching spot on the map.
The effort kilometre puts distance and climbing into a single unit: 1 km of distance is 1 km-effort, and so is 100 m of elevation gain. ITRA uses it to classify trail races; 20 km with 1,000 m of gain makes 30 km-effort.
Estimated duration forecasts walking or riding time from the distance, elevation gain and loss, and a reference speed. On foot, GPX Path for Mac counts 4.5 km/h on the flat, 1 h per 350 m of climb and 1 h per 700 m of descent, then takes the longer of the horizontal and vertical times plus half the other. Breaks are not included.
On the site: GPX Path for Mac
Reference speed is the flat-ground speed used to estimate a duration. In GPX Path for Mac it is set per activity; by default 4.5 km/h on foot, 24 km/h on a road or gravel bike, 14 km/h on a mountain bike. By bike, the app adds 1 h per 700 m of elevation gain, or per 500 m on a mountain bike.
On the site: GPX Path for Mac
Maps and data
OpenStreetMap (OSM) is a free, worldwide geographic database maintained by volunteers: roads, paths, buildings, springs, huts. Its data is under the ODbL licence and underpins OpenTopoMap, BRouter and the site’s place search.
On the site: Map credits: legal notice.
The Open Database License (ODbL) has been the licence of OpenStreetMap data since 12 September 2012, replacing CC-BY-SA 2.0. It lets you copy, adapt and redistribute the data provided you credit “© OpenStreetMap contributors” and share any derived database under the same licence.
OpenTopoMap is a free topographic map drawn from OpenStreetMap data and SRTM relief, in the style of official maps. It is published under CC-BY-SA and is the base map of the site’s tools.
On the site: The GPX viewer uses it.
IGN (the French National Institute of Geographic and Forest Information) is the public body that produces France’s reference maps and geographic data. Since 2021, most of its data has been free, under the Etalab Open Licence 2.0.
On the site: GPX Path for Mac offers IGN base maps.
Plan IGN is IGN’s multi-scale digital map, from a view of the whole world down to about 1:1,000 in France. It is updated every month from the BD TOPO database.
On the site: It is one of the base maps in GPX Path for Mac.
IGN aerial imagery (BD ORTHO) is photography of France corrected to sit exactly on a map (orthophotos), at 20 cm resolution. It comes from aerial surveys renewed every three years.
On the site: Available as a base map in GPX Path for Mac.
RGE ALTI is IGN’s digital terrain model of France, on a 1 m or 5 m grid, under the Open Licence. It describes the shape and elevation of the ground.
On the site: GPX Path for Mac takes its elevations from it in France.
SCAN 25 is the digital version of IGN’s 1:25,000 maps, the ones printed as hiking maps. Downloading is free, but use in a consumer app requires a specific IGN licence: GPX Path does not use it and offers Plan IGN instead.
The Shuttle Radar Topography Mission (SRTM) measured the relief of 80% of Earth’s land, between 60° north and 56° south, from the space shuttle Endeavour in February 2000. Its elevations, one point per arc-second (about 30 m), are distributed free of charge by the USGS; OpenTopoMap uses them for its contour lines and hillshading.
A DTM is a grid of bare-ground elevations, without buildings or vegetation. Mapping tools use it to give each track point an elevation and to draw contour lines and hillshading; the finer the grid, the more detailed the relief.
A tile is a small square image, usually 256 × 256 pixels, which together with its neighbours makes up the map on screen. The map only loads the tiles for the area and zoom level on display.
On the site: Offline maps in GPX Path for Mac save an area’s tiles to disk.
The zoom level sets the scale of a tiled map. At level 0 the whole world fits in a single tile; each level doubles the detail in width and height, so four times as many tiles. At level 15, a tile covers about 1.2 km at the equator.
A contour line joins points of equal elevation. The closer the lines, the steeper the slope; the height between two lines, the contour interval, is given on the map.
On the site: GPX Path for Mac offers them as an overlay.
Hillshading simulates the shadows of the relief under an imaginary light, so valleys and ridges read at a glance. It shows the shape of the terrain, not elevations, which contour lines carry.
Geocoding turns a place name or an address into coordinates; reverse geocoding does the opposite. The site’s place search uses Photon, an open source geocoder built on OpenStreetMap data.
On the site: The home page search uses it.
Routing finds a path between two points along the real network of roads and trails, for a given profile: on foot, by bike, by car. In GPX Path for Mac, each click on the map adds a point and the leg follows the paths, worked out by BRouter.
On the site: GPX Path for Mac
BRouter is a free routing engine (MIT licence), created by Arndt Brenschede, that works on OpenStreetMap data and takes elevation into account. It was designed for cycling; the public brouter.de server is run by volunteers.
Hiking and terrain
A loop is a route that returns to its starting point without retracing its steps. On a loop, elevation gain and loss are equal, give or take a few metres.
An out-and-back route follows the same path there and back, to a summit, a lake or a hut. The total distance is twice the way out; in a GPX file, the track folds back on itself.
A point-to-point route, or traverse, links two different places, from one valley or village to another, without returning to the start. You need to plan the way back (shuttle, public transport); over several days, it becomes a multi-day trek.
Waymarking is the set of painted marks and signposts along a trail. In France, the FFRandonnée code puts white and red on GR® trails, yellow and red on GR® de Pays trails and yellow on PR® trails; a cross marks a wrong turn.
GR® trails (sentiers de grande randonnée) are the long-distance hiking routes approved by the French hiking federation (FFRandonnée), waymarked in white and red and often walked over several days. The GR® name and this waymarking are trademarks registered by the FFRandonnée with INPI. GPX Path does not publish their lines, which the federation distributes (topo-guides, MonGR.fr).
PR® trails (promenade et randonnée) are walking routes for a day or a few hours, waymarked in yellow. Like GR®, PR® is an FFRandonnée trademark.
A grade sums up how hard a hike is. The FFRandonnée grading scores three criteria from 1 to 5: effort, worked out from the GPS track; technicality, based on the size of obstacles; and risk, linked to the danger of a fall or a slip.
The Swiss Alpine Club (SAC) scale grades hikes by terrain and what it demands: sure footing, route finding, alpine experience. It runs from T1, hiking on a well-made path, to T6, difficult alpine hiking, often off-path, with climbing up to grade II. In between: T2 mountain hiking, T3 demanding mountain hiking, T4 alpine hiking, T5 demanding alpine hiking.
In France, the Tourism Code (article D326-1) defines a refuge as public lodging, staffed or not, at altitude in an isolated mountain site, with no access by road or by a public ski lift or cable car. It must always keep a space open to the public, and it holds 150 people at most.
A bivouac is a light, temporary set-up for spending one night outdoors, with or without a small tent. The rules vary from one national park to another: in the core of the Écrins national park, you pitch after 7 pm, leave before 9 am, and stay more than an hour’s walk from the core’s boundary, car parks and roads.
A French national park is made up of one or more core areas (cœurs) and a membership area (aire d’adhésion), under the law of 14 April 2006. The core is the most protected zone: the park’s founding decree sets its own rules there, for instance on bivouacking, dogs or picking plants.