What is the 4a's of tourism?

I'm not sure if this is what you're looking for, but this is what I learnt in school.

1: Attractions (Natural, man-made, cultural, festivals/events)

2: Accessibility (speaks for itself)

3. Amenities (infrastructure and service that efficiently and sufficiently enhance the tourist experience)

4: Ancillary Services (Additional/supplementary services that provide support needed by tourist industry; for example marketing, promotional facilities, tour and travel agencies, etc)

Hope that helped!