HERE Maps API - How to create a custom overlay
This article explains how to create a custom overlay and add data from your own tile server to the map.
For extremely large data sets, it no longer makes sense to add each data point as an individual marker, image or polyline. In situations such as displaying weather or traffic conditions over a map, it would be less processor intensive to retrieve pre-built images from a tiler server rather than re-calculating and adding a large number of mapObjects on to the map display. The cost of making a few extra round trips to retrieve data from a server will be much smaller than the equivalent client side processing of adding hundreds of thousands of objects onto the map.
Unless you own your own map tile source, you will have to comply with the licensing agreement of the map tile provider. In many cases this will mean giving some attribution to the original owner, even if the tiles are being offered without cost. Here is the licensing agreement from the National Library of Scotland used in the example:
"You can embed the map in your own website, display your own markers or mapping data on top of it, use it for research purposes, or create derivative work from it. The only condition is that you must display an attribution to the National Library of Scotland, together with a link to the National Library of Scotland website http://www.nls.uk/ whenever our map is used. If you create derivative work, the documentation of your work must contain this attribution"
Through using the functions in the Code Example it is possible to overlay map tile data over a Nokia map. If the images are returned in the .png format, transparency will be respected and the Nokia Map will show through underneath. - feel free to adapt the code to your own use.