In addition to lots of humans getting dirty with the data, Google's mapping products have the advantage of over a decade of intensive use, correction, and improvements.
There’s a simple answer: people.
For all of Google’s reputation as a data-data-data company, the company’s famed mapping product, which arrived on iOS early this morning, is good for a different reason: people. In reporting earlier this year about how Google builds its maps, I stumbled upon a massive operation requiring vast amounts of human labor. Basically, the company can acquire all kinds of data — from governments, cars driving the streets, satellite imagery, private data stores — but humans must compile all these things. We are the ones who understand the logic of the streets and can embed it into the locations on the map.