The Atlas is the successor to my Quick Tutorial /Sample Terrain guide which has recently become hard to find and had a few minor errors in it. This new tutorial covers everything the old one did but adds in items like installation, roads, and objects. If I have the time, I hope to expand it in the future and include more information about how and why things work. If you find any errors with it please post them here. I will try to check back frequently.
I have removed the download links because Snakeman has it on his editing wiki with a few updates that make things clearer here: https://pmc.editing.wiki/doku.php?id=arma3:terrain:the-atlas-by-jakerod
UPDATE: Snakeman (and I think others) have done a great job creating another tutorial here at the PMC Editing Wiki which is definitely worth checking out after or as a replacement for this one. Here's a link to the forum thread covering the PMC Editing Wiki Terrain Tutorial.