You've seen security cameras everywhere in the public space. How many are there? Where are they? This is information that can be difficult to come by. It's not just criminals that are interested in information on this. It's your fundamental human right to be able to go about your daily life without being monitored and watched at every step. You might think that these cameras are for safety, and they can certainly help make people feel secure. Then it automatically follows that these people should know where they are so that they can plan their lives accordingly. You can help document the location of these security cameras easily using just your iPhone.
For inspiration on why this matters and is important to everyone, this keynote from Jacob Appelbaum at 29C3 is worth watcing:
Check out this instructable about adding security cameras to the Open Street Map (OSM). It goes through all the necessary steps, from setting up an OSM account to adding security camera locations and helpful tips on what kind of details you can add along with the location for maximum benefit.
Now every time you are walking about and look around to see a security camera, you can get your iPhone and check if it has been added to the OSM already, and if not - you can make a contribution!