The Map Chooser is a visual display for where players are located in each Season relative to other boards.
Combined with this is the collectible Map Item. Some Seasons will reward players' exploration (and Boss-defeating prowess) with a Map Item. The Map Item allows even greater choices on the Map Chooser. For one, it allows players to replay the board they just played so they can improve their score. It also allows for travel to distant discovered but unbeaten boards. So instead of having to backtrack and replay the levels between where players are and where they'd like to go, they can skip directly to them.