Previously they licensed TomTom's data and tried to fill in gaps with data from OpenStreetMap and others.
Now they have decided to build their own data set from scratch.
>So a new effort was created to begin generating its own base maps, the very lowest building block of any really good mapping system. After that, Apple would begin layering on living location data, high-resolution satellite imagery and brand new intensely high-resolution image data gathered from its ground cars until it had what it felt was a “best in class” mapping product.
Due to ODbL licence they can't mix OSM data directly with other data.
The ODbL has no restrictions on mixing, unlike the creative commons “no derivies” clause. The ODbL just says that you need to share those changes, and that new database, with everyone else. If we give you OSM data, you should give us back the data you combine with it.
If the other dataset doesn't allow that, then the restriction is from that dataset's licence, not from OSM's ODbL.
Now they have decided to build their own data set from scratch.
>So a new effort was created to begin generating its own base maps, the very lowest building block of any really good mapping system. After that, Apple would begin layering on living location data, high-resolution satellite imagery and brand new intensely high-resolution image data gathered from its ground cars until it had what it felt was a “best in class” mapping product.
https://techcrunch.com/2018/06/29/apple-is-rebuilding-maps-f...
That TechCrunch article has a good overview of their old and new mapping systems.