One of my favourite authors writing about one of my favourite artists, I couldn't resist this. "Journeys are the midwifes of thought", argues Alain De Botton. Introspections which are liable to stall are helped along by the flow of the landscape.
Thinking improves when parts of the mind are given other tasks such as listening to music or following a line of trees. The changing landscape distracts for a time that nervous, censorious, practical part of the mind which is inclined to shut down when it notices something difficult emerging in consciousness and which runs scared of memories, longings etc. and focuses on the impersonal and administrative.
You only have to think of what happens when you've forgotten the pin number at an ATM. You take yourself off on a walk, viewing shop fronts or whatever it takes to distract the practical mind. And sure enough, the pin number is remembered.
According to De Botton, Edward Hopper enjoyed train travel, the dreaminess fostered by the noise and the view from the window, a dreaminess in which we seem to stand outside our normal selves and have access to thoughts and memories that may not arise in more settled circumstances.