In the same way that audio software enables DJs to remix music, combining several songs together to create a new one, modern web technologies allow programmers to mash-up data from websites with relative ease.
When I went looking for a map of ATM locations for my local credit union, I was disappointed to find only an HTML table with a bunch of addresses. Now, I can tell that those are all addresses, and if I were to copy & paste any of them into Google Maps, it would have no problem finding that location on the map. But getting all of them to show up on the same map? A little trickier.