Spiggler is a Google Maps mashup that shows you Twitter messages posted from, or near, your location. The map auto-detects your current location and loads the latest Tweets that have been sent from that location.
If you want to view Tweets for a different part of the world you can simply pan the map or use the site's search option. When you move the map to a new location the map refreshes to show the latest Tweets from that area.
It also possible to view Tweets from a specific Twitter user. If a Twitter user has location sharing turned on you can view their Tweets on the Google Map. The map will display their geo-located Tweets so you can actually view a Twitter user's movements directly on the map. If a user doesn't have location sharing turned on you just see their latest Tweets in the map sidebar.
In the screenshot above you can see one Twitter user's location tracked from northern England, through Wales and down to London. You can view the messages sent from different locations on the journey to London and because the messages are time-stamped you can also see when they were at a specific location.