web mapping - How to create spatial tag clouds or "tag maps"?

I'm looking for implementations of spatial tag clouds or "tag maps". Some papers I found talk about a Yahoo Tag Maps API, but I couldn't find any such thing.

I'd prefer OpenLayers-based solutions, but others would be interesting too.

Edit: Example images can be found at http://www.soi.city.ac.uk/~sbbb717/go2/iv_figs/, e.g: