Show your friends within the garmin unit on the map?

Garmin has had that feature (in some form) for a while.

https://www8.garmin.com/manuals/webhelp/edge1030/EN-US/GUID-0C183A1A-233D-4C26-ABEA-8DFBF6E2A57A.html

I set up my club's website so riders can pin their location and other riders can see the pins (though, not on a map and not live/continuous). That's done through my GRouteLoader app.

Cool! :-D Nice to see, great work!

Yes, actually I want to receive and input different friend locations into the garmin device and show it on the local map.

Some experience regarding import real time locations? Waypoint? POIs?

You can add location (same as waypoints) programmatically. You might be able to do that on a background process. 

The problem is that you can only add new locations.

That is, if you add a location with the same name, it gets added with a number appended. 

There's no option to delete a location.

I'm talking about "system" locations. 

Your app can have its own private locations but I don't think they will be displayed normally.

Aaa. That could be one way forward... lots of waypoints... :-o lol But maybe tweaking these?

Another thing might be to add tracks programmatically?! Have your tried that?

Yeah, you are right... the trick is to be able to use some standard build-in function so the garmin device shows it properly...

You can't tweak them. You can only add them.

You can download courses, which are really tracks. They show up in the courses list.

There's no way of getting them to just show up on the map.

They are also much more data, which you probably don't want to download frequently.

Thanks! I'll try one approach of playing with waypoints then and see where we gets... 

&Freddan