This page will hopefully give you some tips on how to perform common tasks in JOSM.

Select a way sharing common nodes

Quite often you will come across the situation where two or more ways share a common set of nodes. Using the select tool you seem to only be able to select one way.

If you hold down the middle mouse button while the cursor is over the ways you get a pop up listing the ways. If you hold CTRL while the middle mouse button is still held down, you can release the middle mouse button and then use the left mouse button to select one of the ways from the pop up.

How to extend a way

Use the "select" tool (s) and select the end of the existing way. Then, use the "node" tool (a) to draw new nodes which will automatically extend the way.

The revised way will contain the original way plus the new elements and if you named it or added any other attributes the extended way will have those attributes.