When it comes to that sort of fine tuning, there's no substitute for JOSM, which is the all-powerful java-based desktop editor with a hundred plugins and a some

When it comes to that sort of fine tuning, there's no substitute for JOSM, which is the all-powerful java-based desktop editor with a hundred plugins and a somewhat inscrutable UI. But it's great because it can load several sources of aerial imagery at the same time, and quickly cycle between them or set transparency levels. This gives good perspective when it comes to precise alignment of map features to imagery, and to each other.