C# - How can I limit data retrieved when displaying pin on map

I don't have any clue on how to start this.

I have a listing of places saved with Lont/Lat in DataBase. I will shortly have several thousands or even millions of record and I want to display them on a map.

How could I avoid retrieving thousands of records' data when I will cluster them on the map (if several places are in the same area [so based on the zoom level] a pin with the number of element underneath will be displayed).

Thank you.