Its history goes back to Obtiva and Mad Mimi!
Instead of a single queue of stories in a backlog, User Story Mapping organizes stories into a set of big stories (Jeff Patton doesn't like the word "epics") that are the vertebrae of the functionality. These don't get prioritized, they just are.
They are arranged into some kind of left-to-right order, usually by time.
Then the user stories that comprise that are arranged below each big story, like ribs.
As a result it becomes simpler to prioritize—you can look at just one vertebra at a time.
The main idea of User Story Mapping
This shows necessity decreasing with distance from the backbone.
During planning, we look at the current state and what we can do to create desired outcomes later. Minimize the "output" created during this stage to make it as focused as possible on what will create the outcomes.
The thick horizontal purple lines delineate releases .