Seems like it is the developer's location, with the following note from the bottom of the link:

"(However, there's still the caveat that if any app triggers “Snap to Road”, all apps get “Snap to Road”.)"

which seems to be a poor implementation decision vs providing apps snapped or unsnapped location data based on their setting, but may be the result of some early-on ill-considered internal designs?

An indirect and undocumented decision, apparently, based on this somewhat confusing list of "activity types":

https://developer.apple.com/library/ios/documentation/CoreLo...