They do use OpenStreetMaps data and give attribution to them as one of their sources. But if they were to only use OSM's data, people would cry foul that Apple maps is not giving them clear and visible attribution (for e.g. by adding a "OpenStreetMap" label on the map you are viewing in Apple Maps). Right now, except for maps source providers that legally require Apple to provide visible attribution somewhere in their UI, all attributions are tucked away somewhere in the internet - https://gspe21-ssl.ls.apple.com/html/attribution-199.html
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They do use OpenStreetMaps data and give attribution to them as one of their sources. But if they were to only use OSM's data, people would cry foul that Apple maps is not giving them clear and visible attribution (for e.g. by adding a "OpenStreetMap" label on the map you are viewing in Apple Maps). Right now, except for maps source providers that legally require Apple to provide visible attribution somewhere in their UI, all attributions are tucked away somewhere in the internet - https://gspe21-ssl.ls.apple.com/html/attribution-199.html
OpenStreetMaps attribution is visible in the UI; look at the bottom of the screen when you're selecting the mapping overlay.