Data Structure Java, Searching

Using JSFiddle, You will be doing a bit of research for a web company. They want to be able to quickly find what users of an app have visited a geographical location within a certain period of time. The App has the user information and periodically polls and stores the location of the user using the GPS function of the phone. The App collects and stores millions of pieces of information an hour - so search efficiency is extremely important. The company wants you to design a storage scheme for the data that will allow you to quickly and easily determine if a user has visited a specific store or location, how often, and for how long. You must determine how you will store and retrieve the data and what types of data structure and organizational scheme you will use for the data. You will write a one page paper covering the "plan" for the data storage and search techniques that you will use to ensure that you have incredibly fast retrieval of the information for the proposed application. Please save you paper in PDF format before you submit. (be sure to back up your plan with web links and resources - so you will want to do some research. Also you will have to develop an algorithm to effectively determine if someone has actually visited a location - so you will have to think about that too.