Sonu says on a map "up" always means "ahead", the way we are walking

Why

Sonu's mixing up two different 'ups'. On a page, up is wherever your body faces — that changes as you turn. But a map's up isn't about you; by agreement, up on a map means NORTH, a fixed direction that never moves no matter which way you're walking. If up meant 'ahead of me', two people facing different ways would draw the same street opposite ways and no map could be shared. Fixing up as north lets everyone read the same map alike. 'Ahead' is about you; north is about the Earth. Test: turn a map so its top points where you're walking — the printed labels go sideways or upside down, because the map's north didn't move, you did. The sister is right: up on a map is north, a fixed direction — not the way you happen to be heading.