As LibertyImp asked, would this require people to give up their location data? Could people just make accounts representing cities/towns in a decentralized manner, and others could view notes directed toward those accounts? For example, someone makes an account for Boston, others post messages directed to the Boston account of events they are advertising that are going to take place in Boston, and still others view the messages directed to the Boston account when they want to see what is going on in the city. A method like this would also allow people to keep up to date with areas that are not their local areas, and wouldn't require them to give up location data.