To get a PERFECT medal on a particular zone, you need to obtain the maximum score, rescue every survivor and get a gold medal time - all without dying - in a single run.
This trophy requires you to do this on every Critical Urgency (yellow lightning bolt) zone. There are 11 such zones in the game.
This is the list of Critical Urgency zones.
Zone 4 (Goddard's Run)
Zone 10 (Cameron's View)
Zone 14 (Lave)
Zone 21 (Ka D'argo)
Zone 25 (Chiana)
Zone 30 (Aeryn)
Zone 34 (Adams Quadrant)
Zone 38 (Aleksandra Station)
Zone 42 (Lindup Station)
Zone 46 (Almek Front)
Zone 50 (Vilio's Wrath)
This trophy will also come naturally if you're going for Perfectionist.