Birdinia is an imaginary country with a long tradition of birding. Birding consists of observing bird life in the wild, noting when birds come and go, when they breed, how many birds can be found at a given location, and so on. Birders usually enjoy sharing information about which birds they have observed and when and where they observed them.
You are requested to write a notification application for a client. Your client is the National Ornithological Society of Birdinia, and it needs to alert its associates about bird sightings all around the country. Interested people should be able to choose to be alerted about sightings in their preferred area or areas.