The overlay maps are separate to the planning maps and have no effect on route calculations.
Think of them as clear sheets with extra information that you place over the top of the planning map.
The planning map underneath does all of the route calculations.

Each overlay map contains different information. For instance, the OSM overlay shows footpaths and if you zoom in tight there is an incredible level of detail, from post boxes and public toilets to individual trees planted in a city. The Michelin map is famous for its green roads, a road with a green line alongside it indicates a scenic section. Motorway networks are also clearly seen. Google maps are good for showing shops and restaurants. The HERE logistical map is useful for anyone using oversized vehicles as weight and size limits are visible as are environmental zones.

The overlay maps are just additional tools to use while planning your routes.

@Nick-Carthew said:

@Brett-Bartick The fact that the blue route line from OpenStreetMap follows the road precisely is the biggest clue, plus my experience recognises the look of the map. The OSM overlay map has been used as it provides a clear demonstration of the difference between all maps.

Thank you once again for the clear explanation! The information you provided should be part of the online manual. I guess you need to know the details of the application before you can understand the manual.

What's confusing to me and doesn't make sense is the following:
If we are using the HERE map, and we want to ensure that the OSM and TomTom maps route in the same fashion as the HERE map, why would you want or need to use an overlay map? I would have thought you use the HERE overlay (with HERE routing) and make sure the red (TomTom) and blue (OSM) lines follow the black line. If they don't. add shapping points to the route. Why would I need to look at a different overlay if all I am after is making sure the TomTom and OSM routes are the same as the HERE route?

@Nick-Carthew said:

@Brett-Bartick The example shows the overlay map from OpenStreetMap.

I appreciate all the detailed information you provided! Thank you.
How would one know from reading/looking at the example provided that the overlay map was from OpenStreetMap (OSM)? Based on what I read on the support page, I just assumed the overlay map was the HERE map. I don't see anywhere in the documentation page that says the picture is using the OSM overlay map.

Each planning map comes with its own set of algorithms embedded within the map data to calculate which roads to use.

The algorithms are unique to each planning map.

So if you use MRA Navigation Next you should use the HERE planning map.

After choosing the HERE planning map you can also click Always use this map for new routes to set the HERE map as your default planning map.

From now on all new routes will be created using the HERE planning map.

My screenshot below shows the planning map from HERE is selected and also the option to Always use this map for new routes.

The overlay maps are separate to the planning maps and have no effect on route calculations.

Think of them as clear sheets with extra information that you place over the top of the planning map.

The planning map underneath does all of the route calculations.

So with the HERE planning map selected you can then use any of the overlay maps.

If you do not see the same blue menu bar with the planning maps that is shown in my screenshot, click Page menu first and then all of the same options will be available to you.