OpenStreetMap’s power editor JOSM comes with a built-in Validator that helps you ensure your changes are bug free before you upload them to the map. The Validator runs automatically before each upload, but you can also run it at any time during the editing process. It’s a great tool to make sure your edits are rock solid — here’s a walkthrough of how to use it.

Running the Validator

To get started with the Validator tool, you’ll need to:

  • Open the Validator window from the Windows menu in JOSM.
  • Select the data you want to review, and click the Validate button.
  • If no data is selected, the Validator will run on all the data in the current data layer.

Common errors

Once the data validation is complete, a new layer called Validation errors will be added to the Layers panel. Here are some common issues you may encounter:

Error/warning Description Screenshot
Crossing Ways Checks for ways (highway/railway/waterway) that cross each other with no crossing node or intersection
Way end node near other highway Way ends within a few meters of another. These are possibly accidentally unconnected ways
Crossing Buildings Checks if buildings are overlapping
Unconnected nodes with physical tags Checks for invalid unused and untagged nodes
Duplicated nodes Checks if there are nodes in the same location

Fixing errors & warnings

To help with prioritization, nodes and ways will be highlighted based on severity — red for errors and yellow for warnings. Some errors and warnings (Unconnected nodes with physical tags and Duplicated nodes) can be fixed automatically within the Validation panel by clicking Fix.

However, most errors need to be checked and resolved manually. To correct validation errors:

  • Select the first item in the list. Right-click and select Zoom to problem.
  • Click the Select button at the bottom of the Validation window to select the ways or nodes that need altering.
  • Fix the problem based on the category of the error.
  • Rerun the validation tool to check that the issue has been resolved.

Custom validators

JOSM performs validation from a list of predefined rules. If you’d like to focus your validation, you can choose which rules to run, in Preferences > Validator > Tag Checker rules.

Get validating!

Visit our mapping guide to learn more about validation and fixing other common mapping issues. If you have any questions, get in touch on OpenStreetMap or Twitter.