Are the areas in Shadowrun pre-generaled, or are they random every time the game is played...?

Maps are themselves premade and some events are in fixed order however gameplay isn't so it's like chess really, depending on where your team is, what's your skill set, archetype and equipped slots, items fights are never the same. Despite linearity you can do some things in different way (for ex. drones infiltration) or skip whole missions if they are npc-related.