Can I ask how you map the layout? I know nothing about creating circuits but it's something I've always wondered. How can you map the widths, distances, gradients etc without laser scanning it yourself?
E.g. Codemasters version of Castle Combe for TOCA 3 was the worst I've ever seen, did they just take an aerial shot and guess the rest?
Your work looks amazing, just intrigued on how you get it so accurate?