I use Illustrator and GIMP which is a raster software much like Photoshop. GIMP has features that really help in the making of height maps.
Here’s a youtube video showing how I make height maps in GIMP
https://www.youtube.com/watch?v=8bfy-YPIPxY
There’s more to what I do than just that but that’s the basics. I use Illustrator to do 2 Dementional outlines on separate layers and save as a psd file and open it up in GIMP to use various tools to create gradients for height.
I have GIMP set up as my zaplink program and it works good.