I'm using OkCupid, an online-dating and friend-matching site.
I have set the site to show only matches within 5 kilometers of me. Unfortunately, the site seems to be showing me lots of matches who are more than 5 kilometers away. Why is this?
I figured out the answer.
When Americans sign up for OkCupid, the site prompts them for a ZIP code (postal code). So OkCupid has fairly fine-grained knowledge of where they live.
When non-Americans sign up for OkCupid, the site does not prompt for a postal code: only for a city name. OkCupid doesn't know which part of the city they live in.
I live in a big city outside of the United States. Therefore, a 5-kilometre search doesn't just show me users within 5 kilometres of me. It shows me all users within my entire city, even if they are more than 5 kilometres away.