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What is the best method to convert a singlepart shapefile (i.e. one record that contains several non-connected polygons) into a mutlipart shapefile?

For clarification the original question asked how to produce a singlepart featureclass with unique IDs for each spatially non-connected polygons.

The explode method in Advanced Editing or Multipart to Singlepart would give this result.

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1  
What software are you using? –  Aaron Sep 3 '12 at 19:57
    
ArcGIS 10.0/Quantum GIS/GRASS –  BJEBN Sep 3 '12 at 20:25
    
It sounds like you may be confusing singlepart and multipart. Multipart is when you have several polygons that share the same attributes and are stored as one feature/one record in the attribute table. Singlepart is when each polygon has it's own record in the attribute table, even if some of the attributes are identical to other polygons. –  user3461 Sep 4 '12 at 1:58

3 Answers 3

up vote 7 down vote accepted

If you would like to convert a polygon feature class with a single record to a polygon feature class with a record for each polygon, use Multipart to singlepart (Data Management) aka "explode".

To convert single-part polygons to multi-part polygons, you can use the dissolve tool in ArcGIS. Make sure to dissolve by OBJECTID and select "Create multipart features". ArcGIS help also has a section on creating a multipart feature.

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Unfortunately, dissolve is not the tool that I am looking for as this creates dissolves features into multipart features. I have nothing to dissolve and thus it simply creates a copy of the input file... –  BJEBN Sep 3 '12 at 20:04
    
Instead of using the objectid field which is unique to each polygon you should be using a field that groups the polygons into the single multipart. –  Hornbydd Sep 3 '12 at 21:20
    
There are no other attributes besides shape area and shape length... I was hoping that there was someway to make a multipart feature based on spatial extent of the polygons. –  BJEBN Sep 3 '12 at 21:41
    
See my edited answer on how to use Arcgis to do what (I think) you need. –  Alexandre Neto Sep 3 '12 at 23:57
    
+1 for multipart to singlepart (data management) –  user3461 Sep 4 '12 at 2:00

To convert singlepart polygons with one record to multipart polygons, Advanced Editing in ArcGIS can be used. Start Editing session, activate the Advanced Editing and then use Explode Multipart Feature (Note: all the polygons need to be selected).

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Using Quantum GIS, you can use "SingleParts to multipleparts" tool.

Vector > Geometry Tools > Singleparts to Multiplepart

Has you will notice, you can do the opposite in the same menu.

Edit:

Since you have access to ArcGIS you can enter edit mode, select your feature and in the advanced editing toolbar use the explode tool.

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I am not that familiar with Quantum GIS but when I use the singleparts to multiparts function I receive the error "At Least two features must contain the same attribute value. Please choose another field" I only have one feature in my featureclass... –  BJEBN Sep 3 '12 at 20:08
    
I had no problem using the single part to multipart tool with a single feature file. –  Alexandre Neto Sep 4 '12 at 14:49

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