Originally Posted by Erhan
I think this is the part where having a faster GPS unit helps. You get more of those points, each with your coordinate and speed. And I bet external GPS have better accuracy as well.
I think the points of interest (like the turn names/numbers) are just there as a reference for you. The only thing that is crucial is the coordinates of the start finish line, so that HLT can create lap time data. All the rest (speed, position) are just recorded GPS readings.
In fact, if you get out of the track, or do a shortcut and come back to track, you will see that on the google maps as well.
Below pics are taken from HLT's website:
LEFT: iPhone's internal GPS RIGHT: External GPS
Oh nice, I didn't know about that. Thanks for that actually.
So, while still not a requirement, external GPS just became a little bit more nice to have.