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Welcome to the JOSM guide. This guide is split across several tabs (above), starting with an introduction aimed at new users. The text assumes some knowledge of OpenStreetMap concepts, and focuses entirely on using JOSM, not other tools. As such, some users may prefer to read the general Beginners' Guide or the Potlatch 2/Primer or learnosm.org (which also offers JOSM tutorials).
Don't like jar files? Click this java web-start link instead.
For operating system specific installation steps or troubleshooting tips see JOSM/Installation.
When JOSM starts up, the main editing space displays some text. This can include important announcements, but really we want to see some map data …
Finally, use the left mouse button to drag a box around the area you want to download.
You should download an area encompassing the editing you will be doing, but avoid downloading too much map data (the OpenStreetMap server will take a long time to respond, and JOSM may slow down or run out of memory) You probably want to zoom right in close to the maximum zoom level. Pick a handful of streets around the area you are interested in. Start small, because you can download more data as you need it.
When you click 'OK', the data should appear in the main editing area.
Zooming and Panning
Within the main editing area, you can pan around and zoom in and out.
If you can't see anything you probably need to zoom out (scroll backwards) until things come back into view. While zooming in you need to point the mouse at the data you wish to zoom towards.
Yellow hatching (diagonal lines) indicates areas which are not loaded into JOSM at the moment. You should see a rectangular area with a plain black background. This is area you have downloaded. Within this area (and trailing off the edges of it) you will see the OpenStreetMap data.
Download more data
Now that JOSM knows where it is, it's quite easy to request a little bit more data to extend the downloaded area. Use the zooming and panning features described above to position the visible area. The rectangular area of the screen which is currently in view, will be the default selected area next time you click the download toolbar button ()
Try downloading a little bit more data in a second rectangular patch, of about the same size, alongside the area you already downloaded. To do this you will need to zoom in and out until the width of the first downloaded area is about the same as the visible screen width, and then pan off to one side to position the view on some new territory (a patch with yellow hatching), then click download.
This time you don't need to do anything within the download dialog. Just click 'OK'. Zoom out a little bit to see the result.
Remember, always avoid downloading too much data in one go.
Load a local GPX file
Above we described using the download dialog 'slippy map' tab to choose an area to download when we first start JOSM. Another approach is to load in a GPX file before downloading data. If you want to do some editing without using GPS traces, skip this section. Here we will assume you have figured out how to get data off your GPS device and into a GPX file (or NMEA file) on your local disk (See Making GPX Tracks)
When JOSM is displaying a GPS trace, you can zoom and pan using the scrollwheel and right mouse button as described above.
Now you can follow exactly the same procedure to download some map data alongside your GPS trace. As described in the previous section, position the visible area of the screen, and click the download button to get some data. As always, you should take care to avoid downloading too much data. If your GPS trace is from a short walk, then you might typically download an area encompassing the whole thing, but if it is a longer trace, travelling through a dense complex area of the map (e.g. a car journey driving through a city) then this might be too much data. Instead you should zoom in on just one end of your trace and grab a small rectangular area to start with.
Download other people's traces
OpenStreetMap has a database which is separate from the main map data, especially for sharing raw GPS data. You can download any raw GPS data which others have contributed in the area you are looking at. This is an additional tickbox option in the 'Download' dialog.
Working with other people's traces is not required and often may not be very useful, but it can give a useful indication of how accurate your own trace is, and how existing data has been positioned. Where several traces have been taken along the same road, it may be useful to judge the position of an average line, to reduce the inaccuracies of GPS. As well as viewing other people's traces, you can upload your own. Again this is not required.
Switch on aerial imagery as background
Now you're ready to begin some basic editing.