If you triple click a contour edge all the connected edges should select with it. It is not required to weld it. If they don't select, then they need to be connected by hand or ruby.
When you use "Add location", you import a map and terrain from Google Maps. At the same time, the coordinates are saved with your model.
This is a convenient way to attach the coordinates to the model, but if you don't need the terrain you can delete it. If you have a more precise terrain you can use that. Users can write plugins to use other tools for geo-referencing.
