Hi there! I believe what you're searching for is the height maps to the public maps, correct? Unfortunately, these are not accessible as images, so screenshoting and cropping them is the only way to get the heightmap images alone. If that is what you wish to do, simply use the PrtScn button on your keyboard to take a screenshot (You can hit tab to hide all GUI and cursors/tab again to unhide).
Then, locate the screenshot in your Feral Heart Folders (Local Disk>>Feral Heart>>Screenshots) and right click on the image. Click the option "Open with" and open it with a paint program to crop. If you're using a PC with Windows on it, you should automatically have the program called "Paint". Open the image with that and use the Select tool (Looks like a dotted box) to drag and select the area in which you would like to crop to. Once selected, hit Ctrl + X and the image should dissapear. Simply open up a new window of paint, and hit Ctrl + V to paste the image, and then save. Since you are cropping a small window from such a large screenshot, the quality might not be too great, but I believe that this is the only possible way to isolate the heightmap.
Hope this helps! If you have any questions, let me know c: