bridge tag on a node

I think bridges should be mapped as ways wherever possible. If a bridge is just mapped as node, it doesn't show which direction the bridge is going in, or what it is crossing over. Also this means you will get validation tools warning of "intersections without junctions", and without mapping bridges/tunnels as ways you don't know if this is actually an error or not.

Mapping small footbridges does not have to be exact, but you can usually estimate the approximate length, ie is it 1m, 5m, 10m etc. Plus you can tag it appropriately, eg "fixme=estimated length", then someone may map it more precisely later.

Over a ditch? I think I've used bridge=yes on nodes where there's a tiny bridge crossing a stream. This is seams reasonable because it's safe to assume that a footpath would be bridging over a stream rather than the other way around. Also there's little potential for routing confusion. It's not important to know whether you can get down from the footpath to the stream, because firstly you wouldn't normally want a routing system to pick up on streams anyway, and secondly footpaths and streams can be assumed to be accessible to eachother even when there's a bridge involved.

But I think maybe streams (and ditches) are an exception, and we could regard this as a simplified mapping approach, to be refined later.

In the vast majority of bridge mapping situations, it's best to map them as a way, because this captures important information: Which way is bridging over which? How is one accessible from the other? (often some little highway=steps connect separately somewhere)