A related tool I’m working on is a visual debugger for topology construction. You can see an example here showing California state and county boundaries: http:

A related tool I’m working on is a visual debugger for topology construction. You can see an example here showing California state and county boundaries: http://bost.ocks.org/mike/topology/debugger.html http://bost.ocks.org/mike/topology/debugger.html You can zoom & pan in the debugger as well as use the arrow keys to step forward and backward through each step of the construction process, while in the JavaScript console the global `current` gives details on the current step. My plan is to make this a drag-and-drop interface for constructing TopoJSON with the ability to see exactly what’s happening along the way. Of course, it might also be nice to edit and fix the topology in-place, but for now that’s probably better left to desktop GIS!