Studies have shown that the majority of one's social network comes down to a matter of location, and the Crumbler app is designed to capitalize on that fact. The social media platform is based around people leaving 'crumbs' (i.e. location-specific photos or videos) that other users can track down to connect with the people around them.
Most of us feel as though we have a bond with our friends that extends beyond the coincidence of geographical proximity, and yet investigations into social behavior have consistently proven that that doesn't seem to be the case. It's easiest to stay in touch with the people who are physically nearby, despite the connectivity of social media, and humans are inherently wired to go for the easiest solution in all things.