The Bounded Areas operator in the Transform toolbar for drawings will add an area object in every region that is enclosed by lines, including those regions created by lines that intersect themselves.
In the illustrations above, four new areas have been created.
Holes and Islands
The Bounded Areas transform operator will try to resolve regions enclosed by lines within other closed border lines as separate areas. This is a very useful capability when creating lines from closed contours.
Suppose we have one region enclosed by lines that is entirely within another region enclosed by lines. We can select the lines and run the Bounded Areas transform operator from the transform toolbar.
By using Touch Select and touching both areas in turn we can see that the result is two areas have been created. One area is the inner circle and the other area is the larger circle with a "hole" in it where the inner circle area is located.
Creating Areas in Drawings
The Bounded Areas operator is frequently used when we import a data set that consists of lines and we would like to have areas. For example, we might import a drawing that outlines lakes or other regions using lines. We can use such drawings to create areas for lakes.
Suppose we've imported a drawing showing Great Bear Lake in Canada drawn as a boundary line. We can select the lines and run the Bounded Areas transform operator. The drawing is shown with Background turned off in the Layers pane so that the default checkerboard pattern shows through and makes it clear that only lines are involved.
The result is areas created within enclosed lines.
Zooming far into the region in the middle Eastern part of the lake we can deselect the largest area in the lake to see that smaller enclosed regions (representing islands) were created as separate areas by the Bounded Areas operator.
If we wished to create a single area for the lake to use within a map we might not want the other areas and can easily (since they are selected) delete them.
Be careful (and skeptical) when working with drawings that have been imported from CAD systems and other topologically unaware software. Such software might create lines that appear to be closed to form a region, but that upon examination at very high zoom levels will be seen to not connect to form closed regions. If the operator yields unexpected results, examine the lines that were thought to be closed for small breaks. For example, if selected contour lines do not result in neat areas it may be possible that the contour lines are not closed figures.
If the lines involved have data attributes, the created areas will acquire the data in accordance with the transfer rules that have been specified for those data columns.
Transform - Boundaries to create boundary lines from area objects.