Fixing the error of NOT joining ways?

Assuming you're using Potlatch 2:

You can tell which nodes are junctions, and which aren't, because junction nodes have a little black outline box around them.

To join a node to another node directly underneath it, just select the node (you might need to press Enter afterwards to say 'please don't extend the way), and press J for Join.

Alternatively, just drag the node on top of the way you want to join it to, and press J.

Potlatch 2 is also smart enough that if you shift-click a way to insert a point, it will automatically make a junction in any other ways that happen to be passing this point.

This depends on which OSM editor you are using. For this sort of fixing, I would recommend using JOSM.

• If you use the JOSM validator, it will highlight "crossing ways", ie ways that cross on the same layer, and don't share nodes.
• To fix this, you can use the "Draw nodes" mode (the 2nd icon down on the right hand toolbar, or press "A").
• Then if you move the cursor over the crossing point of the two ways, both will be highlighted in green. Then just click to add a node to both ways, which will connect them.

Note: Not all crossing ways should necessarily be connected, only if they physically intersect. If the ways cross on different levels (eg if one is on a bridge or a tunnel), then they should not share a node.Instead you should map a bridge or a tunnel, with appropriate layer tags.