Behind a noun:
- amount of time + ごとに = おきに = every so much time
バスは 15分ごとに出ます。The bus leaves every 15 minutes.
- clock / calendar etc. time + ごとに = every unit of time / day / etc.
私は日曜ごとに教会へ行きます。I go to church every Sunday.
日ごとに暖かくなります。It gets progressively warmer by the day.
- 「ごとに」emphasizes each time/space included, whereas「おきに」emphasizes the amount of time/space skipped. Go to okini (おきに)
この電車は二駅ごとに止まります。 This train stops at every other station.
この電車は二駅おきに止まります。 This train stops at every third station.