What is a User Story Mapping?
Story mapping (Jeff Patton) arranges the backlog in two dimensions: the user's journey flows left to right (the backbone — browse, choose, pay, receive), and detail stacks top to bottom by priority under each step. Slice horizontally and each row is a coherent, end-to-end release.
It fixes the flat backlog's blindness: a ranked list can't show that you've built checkout exquisitely while "receive order" has nothing in it. The map can — at a glance.
Worked example
Mapping a food-delivery product, the backbone reads: find restaurant → order → pay → track → receive. The team's draft backlog piles nine stories under "order" and one thin card under "track." The first release slice forces the correction: one decent story per backbone step beats brilliance in one column — because users don't experience columns, they experience the journey.