[GIS] Calculating area between two line shapes using QGIS

arealinepolygonqgis

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.

Any ideas?

enter image description here

Best Answer

I am not sure I've understood quite correctly, but I imagine you want to calculate the area between these two lines :

enter image description here

If that is the case, why won't you realize two buffers on both lines (with a buffer-distance equal to that of the distance between the two lines) and then have them intersected, the resulting polygone will give you an approximate area.

There will be a problem if the distance between the two lines varies a lot (they're not parallele).

I made a test where :

  1. I created a line layer (and made sure it turns out ill-drawn) and added two lines to it (1),
  2. I then mesured the distance between the two lines and made buffers on both entities with that distance (2),
  3. lastly, I made the intersection of these buffers (3).

If your lines are better-drawn, you can expect a much neater result.

Related Question