A recent study by Justin O'Beirne found that Google Maps remains years ahead of Apple's mapping service, which is to be expected given that Google has had a 6-year head start compared to the tech giant in Cupertino. However, the study shows that Google is ahead of its main rival in a variety of areas, especially in regards to the amount of detail Google Maps contains compared to Apple's solution.
Google's Maps service not only covers a larger landmass in remote areas compared to Apple Maps, but it also does a more thorough job at mapping the same rural areas in much greater detail, to a level where one can tell from a simple chromatic Map whether buildings in the San Francisco area have bay windows. Google actually began mapping 3D buildings back in March 2012 when 1,000 3D landmarks were introduced to Maps. But by October of the same year, the number of buildings represented in 3D in Google Maps rose to a staggering 25 million, and this figure only continued to increase since. The tech giant is able to collect the necessary data for reconstructing buildings from satellite imagery, which is then algorithmically calculated with computer vision techniques in order to recreate accurate 3D representations within Maps. Granted, Apple also offers 3D buildings in its Maps service but not to the extent of Google and generally speaking not in remote areas where the company headquartered in Mountain View has a much bigger presence. Furthermore, the search engine giant also has numerous Street View vehicles that roam the roads around the world and constantly add new content or refresh existing data.
Like Google, the Cupertino giant also offers indoor maps but only in some airports and similar points of interests. Likewise, Apple has its own vans on the road designed to map their surroundings for Apple Maps, but once again this hasn't been done to the same extent as Google, and Apple is likely relying much more on third-party data from services like TomTom. At the end of the day, while Apple's service seems to continue improving every year, Google isn't resting on its laurels either and with every new improvement of Maps, it continues to make it difficult for its rival to catch up.