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I have a shapefile containing the road traffic noise of a city.

The shapefile has 5 columns, where 'noise_in' (noise interval) ranging from 1-5 is included.

I want to remove/mask the road noise from a specific area.

My problem is that the noise intervals covers more than just this area, e.g. if I remove a polygon from the file, covering the area of interest, it will also remove the noise from an adjacent area, which I'm not interested in.

The attribute table looks like this:

enter image description here

The road noise for the area looks like this:

enter image description here

I would like to remove all the road noise from this area, meaning all 5 noise intervals. Unfortunately, I have no available date for recalculating the road noise for the area.

I don't have a polygon for each area.

Here's an example of "Identify Features":enter image description here enter image description here

The red highlighted areas are two different polygons covering large areas of road noise, and I'm only interested in the big blue "vein" in the middle.

I'm using QGIS 1.8 Lisboa for MAC

Thanks in advance

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Do you have a polygon for the area you want to mask? If yes - just clip the layer with noise areas. Or place mask layer above noise layer to mask the area in map composer. –  SS_Rebelious Apr 24 '13 at 10:11
    
I have set in an example of two polygons. –  Kasper Apr 24 '13 at 10:18
    
I still can't understand what is the issue here. Maybe you should try and rephrase the question. –  SS_Rebelious Apr 25 '13 at 15:47
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1 Answer 1

up vote 1 down vote accepted

It appears that you have a shapefile that has overlapping polygons. I'd save each by the 5 road noise categories and then clip out the noise categories you wish to remove.

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Thanks I'll try it out. –  Kasper May 24 '13 at 6:25
    
I have done it another way around. I have made a buffer for the area of interest, clipped out the polygons and created a new vector layer. Here I have the undesired polygons, which there are 286 of. Then I have merged the two layers creating layer with all polygons plus the 286, which are duplicates. Now I just need to remove the duplicates along with the original polygons Any thoughts on this? –  Kasper May 24 '13 at 9:44
    
I'd suggest posting the new question as separate item in Stack Exchange and then it can be easily tackled by the community. –  Zach May 24 '13 at 14:27
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