The API extends the functionality of the HERE Routing API. However, requests must be sent to a separate endpoint.
When you provide modified maps via overlays, the API compiles your changes into routable binary map format. This is the same binary map format that the Platform Data Extension API uses. The Platform Data Extension API creates layers on top of the official map layers.
The Custom Route Extension API stores your changes as overlay maps, so that you can create, modify, and delete them. Similarly, the Routing API also uses these maps.
The API stores the overlay maps in the Custom Location Extension service, where you can view your overlay maps.