Is it possible to create such an application where other users who have this application open can be seen on the map?

Question

Mobile development

Is it possible in theory to create an application on ios and android where other users of the same application can be seen on the map, for whom it is now open, and when it is closed, the user disappears from the map?

Answer 1

Yes. Send data via 3G or mobile Internet to the server, and then send it to the rest.
How to do it? Write code that will perform these operations. How much code do you need to write? Depends on you. It is possible for a day, and it is possible not to write in a year, judging by the formulation of the question. You can also ask "is it theoretically possible to make a rocket?". Yes, you can.

Answer 2

Yes. The server gives the coordinates of these markers (people) on the client, they are drawn, in turn, the client: if requests are sent to the application to the server, the server updates its data for all other clients.