Merging Area Ploygons

This page is designed to help you Merge Area Polygons in ArcView.

Why is it necessary to merge polygons?

Digital Boundary/Cartographic Files contain one or more boundary polygons per geographic area. In the files we are using there are many areas that are comprised of several polygons (such as British Columbia, which includes Vancouver Island and the Queen Charlotte Islands and others). These parts were digitized separately and must be connected electronically. This is required for thematic mapping activities where data tables will be joined to the boundary theme table. Without merging, the mapping results can be misleading due to the way the data would be used for creating classification

Merging Area Polygons:

  • Open ArcView. (from the start menu, scroll up to Programs, and look for a folder called ArcView version 3.1)
  • Start with a new view and add the theme you wish to use in this example.

  • When the theme is loaded, display it in ArcView by clicking on the box next to it.
  • Click on the Provinces name in the Table of Contents to make the theme active.

  • Select Theme > Convert to Shapefile....
  • Navigate to a folder where you'd like to save the theme.
  • Enter a filename (provinces2.shp) in the Convert Provinces dialogue window. Click OK.

  • Add the shapefile to View1 when asked. Click yes.

  • Click on the provinces2.shp theme name in the Table of Contents and make the theme active.

  • Open the corresponding Attribute Table by selecting Theme > Table.
  • Select the name of the geographic code on which the polygons will be "merged". Select Pruid and it will become highlighted

  • Select Field > Summarize.

  • The Summary Table Definition dialogue box opens.
  • Click the Save As... button and navigate to the folder where you'd like to save the file. Name the file Prov.dbf. Click OK. The Merge operation will create a new shape file with the name you provide.

  • In the Field box, select Shape.
    In the Summarize by box, select Merge.
    Click the Add button.

  • In the Field box, select Prename.
    In the Summarize by box, select First.
    Click the Add button.

  • In the Field box, select Prfname.
    In the Summarize by box, select First.
    Click the Add button.

  • Click OK when completed.
  • Add to View1 When asked by clicking OK.

  • Open Theme Table to see the Attributes of Prov Table and view the data in the new theme we created.

  • You'll notice that the new table is smaller and has only 14 fields compared to the other table. (This is useful because it is now easier to select the themes in the View).

back to the top.

For Assistance email libgis@uoguelph.ca.