One of the things you have to accept as a tech writer is being on the receiving end of a never-ending stream of PR pitches. Generally, they’re ill-targeted or irrelevant to the topics I actually write about—for instance, anything with “blockchain” gets deleted immediately. Sometimes, though, a pitch email will be intriguing enough to warrant a reply other than “sorry, this isn’t for Ars.”

Those replies usually lead to an interesting conversation with an expert in a particular field, which is useful for informing our reporting. But the email that sparked this article was about a new navigation app, called Live Roads, that promises to be the first to feature an HD map and much greater accuracy than we’re accustomed to in our cellphones.

Smartphone GPS is usually only accurate to about 4m (13 feet), so the idea of a smartphone navigation app capable of much more accurate spatial resolution piqued my interest enough to try it out. Then it got me wondering how the whole thing works.