Mash-ups are websites that combine content from more than one source into a new integrated source. Mash-ups have become popular with online mapping websites such as Google Maps. Lots of different sites have sprung up to cater for different 'mash-up' tastes, for example Celebrity Maps (www.celebrity-maps.com) lets you find the address of your favourites celebrity's abode.
Now Whereis (www.whereis.com.au), the leading Australian digital mapping and navigation website have released a set of API's (conduits that let developers access data) that let developers access the same map data that is presented on whereis.com.au (and all the other Sensis web properties like whitepages.com.au and yellowpages.com.au). If you are a developer the Whereis API can be accessed from the Whereis Workshop.
There are already some great examples of mash-ups available. My favourite so far is a mash-up called 'My Places'. At 'My Places' you create and edit your own groups of places, and add images and text that can be viewed by clicking an icon on the map. Visitors to My Places have already added lots of great information to the map, for instance I found an entry called 'Quest for best pancakes' that took me to a map of Melbourne with eight 'food' icons representing places to eat pancakes around Melbourne.
Whereis API's are still young but I'd expect to start seeing lots of different mash-ups in the future when developers realise their potential. I'm excited for the time when someone creates a mash-up with all the cafes in Melbourne. Imagine being able to access this sort of data via your mobile phone when you are wondering the streets looking for a hit of caffeine.