There’s no wrong/right side to garter. They’re the same. Every purl-looking row is a ridge. Of if you want to count rows, each purl row is one and the space between is another (it’s a knit row but it looks buried between the purls.)
Jan, that’s a GREAT illustration. Honestly, it’s something I’ve always wondered too!! I never work in garter stitch now (not if I can help it) so never really have the need to count ridges but I never really knew what that meant either!