Dissolve is another very useful function that merges several features together, based on their attributes. All features within a given vector layer containing the same attribute value will be combined to one single feature (one entry in the Attribute table). Shared borders between these geometries will disappear and in the case of spatially divided (geometrically non-adjacent) input features, the result will be a so-called “multipart” feature. The Dissolve (Data Management) tool is useful for portraying or visualizing specific information from a shapefile. For example, here we used the commune_boundary layer for Switzerland (basically the same as the commune_boundary_FR layer, but for all of Switzerland). The geometry of the layer currently represents the communes of Switzerland, but we want to visualize countries instead of communes. In the attribute table, there is a column indicating which country each commune belongs to, thus we can “dissolve” the administrative boundaries based on that field. In the next example, the attributes in the commune layer will be dissolved to create a new layer based on the country geometry. NOTE: Here we will use a layer that has not been provided in the tutorial. This is to illustrate what might be done using the dissolve tool.
To use the dissolve tool (Fig. 32):
- Type “dissolve” into the Search window (or browse to Data Management Tools > Generalization > Dissolve in the ArcToolbox).
- Select the Dissolve (Data Management) tool.
- The Input features will be the commune_boundary (for all of Switzerland) in this case.
- Name and save the output layer as a shapefile.
- In this case we will dissolve based on the COUNTRY attribute.
- Leave the default options for the remaining.
- Click OK.
The result (Fig. 33) shows that the geometry and the attributes represent
only the countries.
Fig. 32. The dialog box of the Dissolve tool.
Fig. 33. The results of the dissolving by the COUNTRY attribute. Reproduced with permission of Swisstopo (BA13016).