If your using KDE you need to modify the ALT key behaviour

Open Control Center --> Desktop --> Window Behaviour --> Actions

And change the modifire to key to something else

Validation plugin

Ensure the validation plugin display is visible by either clicking on the Blue Check Box on the left menu or typing Alt-V to toggle the display

To validate the map you can either select individual ways by hitting the S key and clicking on the way or for multiple ways hold down the shift key while clicking on ways. Or optionally you could enter Ctrl-A to select all objects As ways are selected they will turn yellow.

To remove overlapping ways:

When you expand and highlight the over lapping nodes the over lapping ways should turn blue Hit the D key to remove the offending way

If the wrong way is deleted type ctrl-Z to undo the delete operation To switch to the the "other" way

Middle click on the blue way this will hopefully show multiply ways Hold down the ctrl key this will hold the way list open so you can release the middle mouse button Continue holding the ctrl key down and mouse over the next way description and left click on it's description Then hit the "D" key to delete the way

You may need to recreate part of the way if the overlapping way

To correct crossing ways

When you expand and highlight the crossing way nodes the crossing ways should turn into a fat yellow line. You can now zoom in to the offending area. You now need to get out of this modes Hit the S key for select and click on something else to "reset the map"s you need to get Then zoom until the yellow highlighting disappears. Hit N for new node and click on the intersection to add a new node. A yellow dot (new node) should appear to join the ways.

When your done, don't forget to hit the Z key to get out of adding node mode.