Recording GPS tracks
Lots of raw data are needed to be able to create a good map. A major source of information are the data produced by collecting the tracklogs from GPS Receivers.
To record such tracks, you will need a GPS unit with this function — a specialized unit, but a PDA or a mobile phone are also good candidates. See also the GPS_Reviews and the hardware guide for more information. You will also need to transfer the tracks to your computer, typically using USB or Bluetooth for modern devices.
These tracks are useful even if you don't plan to mark up the roads yourself: There are people without GPS units who will do this if you don't. Tracklogs of roads that have already been mapped are also useful, as they can help to validate the true path of a road by providing more sample points.
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Prerequisites and setup
- Check if your GPS unit has a "Snap to road" or "Lock on road" option, make sure that option is switched OFF, or you will end up merely recording a direct copy of the map loaded into the GPS unit, which is not only a copyright infringement (unless your map was downloaded or derived from OpenStreetmap), but is possibly going to be less accurate than the track you would otherwise record. On Garmin devices, it's on the first page of the map setup.
- Set the position-recording frequency to the highest possible, depending on the memory of your device, the foreseen length of your track, and the speed at which you're travelling. If possible, set it to "every second".
- If you want to update the OSM map yourself afterward, take what you need to record the details of what you encounter along your track — notepad, voice recorder, digital or video camera, etc. Software such as JOSM will allow you to synchronize your recordings with your path, for example, place the pictures on the map where you took them.
Record the track
Go for a walk or a cycle ride or a drive (or whenever you take any kind of journey)
- Take your GPS with you.
- Switch your GPS on at the start of the part of the journey that you want to map
- before you move, wait for a very good fix, i.e., until your GPS has locked as many satellites as possible. (See below for technical details.)
- Clear any track recorded previously, especially if the previous step recorded many false points.
- If necessary, set the GPS to tracking mode so that it records your journey.
- If you plan to make up the roads later, take notes of the street names and other features, unless you already know them. You cannot later get them from or check them on a map, as this would infringe copyright.
- Record your route along any linear feature — rivers and waterways, footpaths, bridleways, rail and tramways, and any other fixed linear features are of interest to OSM. We want points of interest and area information also, so add this information in your travels where you can.
- If supported by your device, you can record waypoints, too, to mark roundabouts, churches, starts and ends of bridges, etc.
Upload the tracks
To upload your tracks, they must be in GPX format, so you may need to convert them. You may also want to edit the tracks before uploading them. There are several options that determine whether other people can see your traces. (See visibility of GPS traces.)
Going further
If you like to contribute more than just the tracks — which already is a huge contribution — then convert them into ways. See the Beginners' guide for details.
Other means to get data for mapping are described on Mapping techniques.
FAQ
See the dedicated page.
Notes on GPS reception
In vehicles
If you plan to record a track from a vehicle, get a very good fix before you enter it. This is especially true for newer trains, where you might well never get one otherwise.
When do you know reception is good?
A 3D fix is not a sufficient criterion of quality. The PDOP is an indicator of the precision of the GPS measure (Position Dilution of Precision). If it is higher than 6 you can consider that you don't have a good fix. Under 4, it is good enough for OSM tracking. Less than 2 means you have a very good fix. The quality of the DOP depends on the GPS capacity of correcting the satellite's signal. You can have a good DOP with only a 2D fix.
