Chapter 7: Application Outlook 293 route. The map information is usually stored on a memory card, which allows purchasing new maps and, by switching to another card when necessary, using the device anywhere. Some handheld GPS devices may also include secondary features, such as Garmin GPSMAP 60c, which contains information for geocaching, GPS–based treasure 8 hunting, and a few geolocation games. A barometer and a compass are other typical hardware additions to a GPS receiver. For other devices, such as mobile phones and palmtop computers, separate GPS modules are available. For instance, Nokia LD-3W is an external GPS module that connects to the phone wirelessly via Blue- tooth. The location information provided by the GPS receiver is then available to application developers. The decrease in price combined with increase in functionality has boosted the sales of personal hand- held navigators, making them common in outdoor activities such as fi shing, trekking, and hunting. As far as wayfi nding is concerned, there are several kinds of personal content created and used, either explicitly or implicitly. The targets (fi nal destinations) are typical examples of user-created content, whereas the routes are often suggested by the application, even though in many cases the user may defi ne the preferences for choosing a particular route. Similarly, waypoints (sub-targets along the route) are implicitly created. Furthermore, POIs are closely related to navigation as, for instance, user-created waypoints. Typically, personal content related to wayfi nding is not heavily maintained. The content is created either explicitly or implicitly. It is then enjoyed, in many cases implicitly, such as by reaching a target, and only occasionally shared. The expected lifespan of wayfi nding- related personal content is often short – when moving in familiar environment, navigation is rarely needed, and once a destination has been reached, there is usually no need to store the related information, unless there is a need to navigate to the same destination in the future. In many cases, the importance of the stored information is low, since the same information can be easily re-obtained. 7.2.3 Annotations Annotations, or tags (or virtual graffi tis), are a typical form of location- based personal content. In its simplest form, an application may allow adding location-dependent notes that can be later locally retrieved and presented by overlaying them on a map. More advanced annotation concepts provide tools for sharing and publishing the annotations, that 8 http://www.geocaching.com/