A Dissolver combines area features if they share a common border and if the attributes selected in the Group By box have the same values. The resulting feature will only retain the attributes that were selected in the Group By box. The borders that have been removed are output through the Unused Lines port.
In Dissolver has an option to dissolve overlapping polygons, as well adjoining polygons.
In case no attributes are specified for the Group By, the Dissolver will combine all area features that touch each other.
The attached FME Template(Dissolver Example.fmwt) shows an example use of the Dissolver transformer.
In this example (like the Bufferer example) a GPS dataset consists of a number of waypoints. The waypoints are buffered, where the buffer size is proportional to the vehicle speed at that point. The idea is to show areas where vehicle speed is low to indicate possible areas of traffic congestion. In this example the data is classified and the Dissolver used to create areas of similar traffic speed.
The red areas indicate congested traffic, blue is slow traffic and green is normal moving traffic...