It's quite simple, actually. The average daily costs for all of the cities and countries around the world come from other travelers.
Here's how it works:
It's like a Wiki for travel costs.
For example, here's a trip budget created for a vacation: A Week In Tokyo.
And here are average daily costs for Paris calculated from many different trips.
So, by signing up and entering your expenses, you can contribute to the average costs and help other travelers. Of course, you also get to organize your budget and see charts, graphs, and tables of your trip finances. You'll even get to view a map of where you went.
