This is neat:
In the lower left corner you can click on "historical" and then dial back the date and time to check out your previous flights. The coverage is best closer to YVR, but once you pop up through the "dead zone" around Langley you'll see yourself. Unfortunately (or maybe fortunately?) the coverage only goes to just east of Langley.
Watching this for a while makes it quite clear where the dead areas in coverage are near Langley. It's quite instructive.