Dissolving polygon boundaries using symbol level drawing

Often, you will want to merge adjacent polygons that share common values in your layer display—for example, you can create a map of states by dissolving county boundaries using their state name attribute field.

Using symbol level drawing to dissolve polygon boundaries

Here are the steps for the simple example above:

  1. Open the Layer Properties dialog box and click the Symbology tab.
  2. Select Categories and click Unique values.
  3. In the Value Field drop-down menu, click the State Name field.
  4. Click the Add All Values button.
  5. Click the Symbol column heading and click Properties for All Symbols.

    This displays the Symbol Selector dialog box in which you can set a number of symbol properties. In this case, you edit the symbols used for the layer.

    The Symbol Selector dialog box

  6. Click the Edit Symbol button to open the Symbol Property Editor dialog box.
    The Symbol Property Editor dialog box
  7. Click the + button to add an empty symbol layer.
  8. Click the top symbol level and specify an outline width of zero.
  9. Click the small lock symbol next to the top symbol level to unlock this level.
  10. Click the bottom symbol level.
  11. Click the Color drop-down list and click No Color.
  12. Click the Outline Color drop-down list and select a color.
  13. Specify an Outline Width as you want it to appear on your map.
  14. Click the small lock symbol next to the bottom level to lock this level.
  15. Click OK to apply these symbol edits and to close the Symbol Property Editor dialog box.
  16. Click OK to close the Symbol Selector dialog box.
  17. Click the Color Ramp drop-down list and choose a color ramp.
  18. Click the Advanced button and click Symbol Levels.
  19. Turn on Symbol Level Drawing by checking Draw this layer using the symbol levels specified below.
  20. Check Join on for all your symbols. Use CTRL and click the check boxes to turn Join or Merge on or off for all symbols in the list.
  21. Uncheck Merge for all your symbols.
    Turning Join on for all symbols
  22. Click OK to accept changes and close the Symbol Levels dialog box.
  23. Click OK to accept changes and close the Layer Properties dialog box.

Related Topics