Create a new layer from overlap between two layers?

Question

I'm new to desktop GIS, and will try to ask while lacking the proper terms from the GIS lingo:

If QGIS was like Photoshop I would like to make a selection from one layer, and then match that selection to another layer to get the overlap between the two and create a new layer from this overlap.

Formulated in another way:

I want to select all land from each of the Norwegian municipalities. In the shapefile I have (you can download it here: http://www.statkart.no/?module=Files;action=File.getFile;ID=41973) municipality borders are found as "N5000_AdministrativGrense" (just the borders) and "N5000_AdministrativFlate" (borders and the land within each municipality). This data (borders and land per municipality) is too administrative - it includes ocean and we have a lot of fjords in Norway. I need the landmass minus ocean.

The landmass is found in the layer "N5000_ArealdekkeFlate" - or so it looks to a novice at least.

So - I want to find the intersection between the landmass (only land, no ocean) and municipality borders and make a new layer that is all municipalities without ocean.

I'm on a mac with QGIS as my installed tool. All tips, pointers and help is much appreciated.

Answer 1

You can do it with the Vector tools built into the newer versions of QGIS.

I am using 1.8 at the moment, and it has a Vector menu.

Got to: Vector > Geoprocessing Tools > Intersect.

Alternatively, you can probably devise query on the attribute table that will select just the features you want. Once selected you can export that to another layer.

Answer 2

If you use the GRASS GIS toolbox within QGIS, then you can do the job with the v.overlay tool. For a quickstarter, see http://grass.osgeo.org/wiki/QGIS_GRASS_Cookbook

Answer 3

In the Processing toolbox there is an option under QGIS geoalgorithms/Vector selection tools 'Select by location'. With this option you can select the features that are overlapping, intersecting and/or touching. The features can be saved to a new file by right-clicking the layer and choosing Save as. Check 'Save only selected features'.

I find this method useful, because it does not merge the attributes of the two layers.