Earthslicer is a game of capturing territory. To make a capture, you must surround an area that is not yet captured. You do this by physically moving through a path that creates some kind of closed loop, such as a circle. The GPS in your iPhone will leave a trail behind you as you move. This trail appears as hollow blue squares. When you complete a closed-off section of the world, it will fill in this area, and you will own it forever. You get points based on the amount of territory captured.
The first question everyone asks is this: can't I just fly/drive around the city/state/world and capture everything? Nope. The maximum area you can capture at a time is about two miles square. In the iPhone application, you will see an orange box extended from your current location, about a mile or two out. This shows the area you can currently interact with. If someone could slice the whole world in one go, the game wouldn't be very interesting!
The slider at the bottom of your application, labeled 'Tracking', controls whether or not the map moves along with you.
After an area has been captured, either by you or another player, you can extend it by completing another loop that partially uses the existing capture as a border. Note that an area cannot be taken away once it is captured!
The bar in the upper-left shows the strength of your location signal. If it's green or yellow, you're probably in good enough shape to make a smooth trail. This indicates you're getting a solid GPS signal.
All slices you make get uploaded to the server, but if you happen to be offline at the time of slicing, the data will be uploaded next time you start the application.
As you move around, running Earthslicer, the application makes occasional requests to the server to get information about your environment, even when you're not currently completing a slice. The only identifying information sent about you is a hash of your device ID. This information is not shared with any other users, but in any case, there is no way for anyone to link this hash to any personal information about you, such as a real name.
However, you should be aware that people can see what Earthslicer user ID has made each slice, and at what time. If you wear a tin-foil hat, you may wish to keep this in mind.