Thanks Alex. That worked
I would like to make a suggestion. The resulting terrain does not exactly match the sizes entered. If I did one tile over a 12km^2 area, the terrain dimensions varied up to 80 metres.
To create tiles that were exactly 512x512 for this large area, I had to adjust the co-ordinates, and build several times, until the resulting tiles were the correct size.
I don't know how the underlying mechanics work. But it might help others if it were possible to set the tile size that you want to generate.
This only became an issue for me because I started using "Path Painter II" from the asset store. Apparently having rectangular terrain tiles is not efficient, because unity always creates a square terrain tile and then squishes it to create the rectangular size. Path Painter II forces you to have square tiles. I have copied a link that explains this below:
https://3dhaven.freshdesk.com/support/s … -terrains-