I am working with population data organised in parish units for the whole of Denmark. Many parishes are very small (ie <500 inhabitants compared to a median of around 1500) so I plan to merge these with the next largest adjacent parish. I am working with shapefiles and can manually merge the polygons using QGIS, but with over 1000 small parishes, it would be nice to be able to automate this process! Any suggestions as to how - in QGIS or other software (I also have access to ArcInfo)?
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Note also the linked questions on the right side of the page at that possible duplicate. Several of them have some discussion on how this is something of an arbitrary problem and thus difficult to do in an automated fashion without more constraints or it can skew resulting data/geography relationships.– Chris WCommented Apr 26, 2015 at 10:00
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1 Answer
You will have to go through several process.
Here are a few indications to help your out.
- First create a new column in your layer BIG_ID_COLUMN.
- Update this column with the Id of each parishes
- Create a new shapefileBIG_SHAPEFILE with the largest parishes and one for the small ones SMALL_SHAPEFILE
- Use a closest neighbor tool (v.distance ; grass) or follow this : tutorial
- Update the SMALL_SHAPEFILE newly created column BIG_ID_COLUMN..
- Then merge the initial layer with : vector -> geoprocessing tools --> dissolve:
select the shapefile and field (NEW_COLUMN in your case), choose name for new shapefile and you are done !
Several different methode exists of course, this is just one of them
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Thanks Juls for your response - that was very helpful particularly as i am new to GIS and needed something straightforward to get me started. Having got a bit further with this I now appreciate Chris W comments that the problem needs to be further defined and, following the suggested links, i eventually settled on the AZtool: geodata.soton.ac.uk/software/AZTool Many thanks Peter Commented May 5, 2015 at 9:10