SatNav is short for Satelite Navigation and is normally associated with car trips. The SatNav Apps do in fact offer a "Walking Option" but generally that simply replicates the car trip at a slower rate. However it seems that there is Google commonality with the emerging Trekker application and these walking trails, paths, ways and track sections are being increasingly included as elements capable of being used by a SatNav device.
The SatNav aim of these Multi-Apps is to provide the Walker with a pre-programmed SatNav Route that replicates the markers he/she will be able to follow "on the trail" and it is emphasised that the walker should always use these ground markers as the primary directional aid. However the SatNav device (SmartPhone etc) using this Multi-App provides a great amount of informational aid for a walker.
Now it is quite unusual if a walker can call up a segment of a Path simply by inputting the start/end points as a car driver might do. This is because the device is generally looking for the shortest route between two points whereas routes such as The Thames Path tend to use "the path less trodden" which can quite often double the length of the trip. So we try to "bend" the route to match the official directions including all the "zigs & zags".
this Icon (or this one for reverse direction) at the top of a particular Walk Map in Frame 3 says we WERE able to program a SatNav route that replicates the official route (or very close to it).
this Icon (or no Icon at all) says that at the last upload of this Multi-App to the Web we were NOT able to program some parts of that Walk but were in the process of requesting such Edits with Google under the Google Local Guides facility.