What Is the Custom Route Extension API?
The HERE Custom Route Extension API is a REST API that allows you to request routes on a custom road network using overlay maps that you have modified.
You can submit overlay maps with modifications, such as block road links, remove restrictions from road links, or insert new road links into the network. The modifications that you submit, as part of your overlay maps, are only visible to you but not to other customers. Also, these modifications are not uploaded to the official HERE map.