How to make a calculator on a map?

Question

PHP

Good afternoon! The bottom line is that there is a list of objects and the cost of its maintenance, and there are people who serve these objects.
The point is to put it all on the map.
The manager enters the map, sees all the objects on the map, can select several objects or an area, and the total cost and number of objects will be displayed so
that it would be possible to understand from the outside which service manager can add objects to which it can be removed.
Maybe there are some ideas on how to implement this, at least directions, or maybe there are already some ready-made templates or examples. I will be very grateful.
There are php and js knowledge, not great, but there is

Answer 1

https://jsfiddle.net/bfgdrc26/59/ - As a simple example, everything is painted with comments