Google updates their maps via 4 ways.
1. They have partners from whom they license data. They do this for countries where they do not have a large presence. China is an example of this.
2. They send out cars with cameras and GPS to take photos of pretty much all major metropolitan areas and suburban areas.
3. They use satellite imagery to help them make corrections if needed.
4. They use crowd sourcing to help them keep up with POI and rapid changes to roads
Apple has Tom Tom as their partner, who generally does a very good job in the areas they have a large presence. They have other partners of course. I believe in China, they have partnered with a company called Gaode. They also use satellite imagery to make corrections to major roads and large POI. Finally, they also use crowd sourcing to help them correct POI, addresses, and incorrect street information. Crowd sourcing really has been the difference for Google in making their maps as good as it is. You have to remember, they've had as many as almost 400 million iOS users, and probably at least that many Android users moving around and helping them make corrections for the past 4 years. Give Apple some time, some data, and Apple's maps will improve in short order. One thing Apple will still lack though, is Street View, since that would require Apple to send out cars to literally take photos.