Importing Custom Heightmaps
Importing a Custom Heightmap is quite simple. The process is initiated from the New Landscape section of the Landscape Modes panel. To active it, select the radio box labeled Import from File to expose the ability to import a heightmap from a file.

To select a Heightmap to import, press the button next to the box that says "Please specify a heightmap", and then select your Heightmap using the file browser.

Now let's try importing a custom height map. For this example, we will be using the image below.

Make sure you right-click Save as on the image (above) to download it to your PC.
Once you have the heightmap saved to your PC, it is now time to use it in the Landscape tools.
Open up the Landscape tool and go into Manage Mode.

Selected the option to Import from File.

Select the Heightmap you want to import from the Heightmap File section.

When the above has been completed, press the Import button to create a new Landscape based off of your heightmap.

Before pressing the Import Button:
After pressing the Import Button:
Now you have a new Landscape to work with that is based off the Heightmap that you just imported.