Who says your smart phone is going to work in an area that just had a big earthquake? The power might be out, the cell towers could have fallen down, or everyone could be trying to use the system simultaneously to tell their families that they&#x27;re still alive. (In some parts of the world, they may never have had cellular service at all! Or they may not be able to afford phones that can run this app.)<p>For example, it was nearly impossible to use a cellphone in downtown NYC in the aftermath of the 9&#x2F;11 attack.<p>The backup plan would be to have a local copy of the database cached on everyone&#x27;s phone, but that would take up a lot of space.<p>Also, who is going to translate the database into every language used in the world? Three English words would be as hard for a Chinese speaker to remember as a pair of geographical coordinates.