Please explain the flight route from London to San Francisco which first goes north to Scotland first THEN west and through Canada?

The flights follow the shortest route, which is over the top of the earth. It looks odd on a flat map, but makes perfect sense if you have a globe of the earth handy. Use a piece of string and find the shortest route between London and San Francisco - it is almost due North of London.

This is known as a "great circle" route.