One of the challenges of writing TUBE is orienting it in space and time, and situating it on the train according to the train schedule, the stations, the distance between them, the geographical location, the climate, and all that. Before I start writing a scene, I always have to reorient myself. Where is the scene happening? On a station? Between stations? How many kilometers away? What time of day is it? How fast is the train moving? And so on.
Of course, when the book will be read, the readers will hardly notice it. But they will trust the story if I keep all the details as authentic as possible. Google Maps is my savior.