This is question asked to me by an interviewer, in which a map of world is given, and for those country you want to send message, just marked circle on that area, and just send to all the people comes in that area. Question visual link is : Design this application The approach that I told him: Firstly build whole person's data (contacts , place information and all) Then where you mark on the map, just build a cluster of that country using Hadoop and fire the message to all the person's contact comes in that cluster. So help me for better understandings of this problem, and if have another good approach (all back-end ad front-end) , then please tell me or discuss here with me. Thanks in advance.