I'm new to using QGIS (2.0).
I'm trying to calculate the sidewalk area of a city.
For that I have some shapes, extracted from Bentley Microstation, with the topology (facades, fords, fences, etc...), but they are in line shapes.
I have merged them in only two shapes: exterior line and interior line limits.
I've tried to convert them to polygon, with the idea to use the "difference" tool after that, but I wasn't able to do it.
I tried to use: "Geometry tools --> Lines to polygon" but it doesn't work, causing lots of holes and mistakes. "Geoprocessing tools --> Convex hull(s)" is not the way because I will need to do so many polygons and it will be an incredible waste of time.