In this example, the landscape chosen for Fill Mode is swamp, which is given in the Draw Type Name slot. The draw program is in fill mode because the center button says Go to draw mode. (The second button functions as a toggle switch between draw mode and fill mode.

While the draw program is in fill mode, a forest hex on the edge of a larger forest is clicked. As can be seen all contiguous forest hexes are turned into swamp as well.

The remainder of the forest on the east side of the map was not changed to swamp because there is a break due to the clear hex by the river. Also note that the river did not stop the fill.