Split branched objects into simple (non-branched) objects. For example, a single, branched area object composed of three "islands" will be split into three separate area objects.
Example
Many drawings will show a mainland region and islands as composed of the same area object. If we wish to delete some of the islands we might first want to use decompose to convert the single, complex, branched area object into many unbranched objects. We can then delete the unbranched objects quickly.
Suppose we have such a drawing. If we click with select touch on any of the "areas" we see they are all selected.
All of the "areas" are selected at once because they are all part of the same area object. We can use decompose to split them apart.
To do so, we load up the transform toolbar as seen above and push Apply.
Thereafter, if we click with select touch on any of the areas we see that only the object touched is selected. This is because all of the "objects" we see are now truly separate area objects.
Note: some GIS systems may refer to this function as "explode."