Once you've established your customer personas, the next step to make your Journey Map is to think of your Map as the total of all stages a customer may go through in relation to your brand.
Again, most marketers traditionally assumed that this begins with your homepage, or by walking into your store for the first time.
However, it's best to identify all the different ways someone can arrive at your brand as a whole, and what steps they may go through before purchasing or leaving and starting again.
For example, take the case of a restaurant. A customer could have initially heard about it from a friend or an ad. Different stages could include: arriving to the restaurant, looking at the menu, ordering food, leaving the restaurant, the wait staff, the feel of the room, and much more. That entire experience is "the restaurant" in the mind of the customer. This is an integral part of the Journey Map.