Many location-based mobile apps track user location for providing services. As a developer embarking on such a project, I found it useful to use the supply side vs demand side classification.
The user population usually consists of suppliers and consumers. For example, taxi drivers and passengers for apps like Uber. Mobile apps track suppliers continuously but request the consider location only upon demanding a service.
A mobile app is generally backed by a server that stores ongoing suppliers location. Such a real-time location map is used either automatically by a supplier allocation algorithm, manually by suppliers to select a particular demand to which they want to answer, or by administrators to manually allocate suppliers to demand, or both. Gett uses both of these, where in particular cases, its customer service representative may manually allocated a supplier to a consumer.
A mobile app can support the demand side, serving the consumer, or the supply side, serving the supplier. The supply side app will exhibit real-time demand, so that suppliers can respond to demand and plan their behavior (go to regions with dense demand). The demand side app is mainly used to request a service, and often will display the current supply situation on a map, and once a particular supplier is chosen track its progress on a map.
In a field service organization app, the demand side app will usually not exist, but consumes may be provided with a link to a live map (a web app) tracking the supplier progress along the route to the consumer.
One might consider the construction of a generic tracking app. Seems that the supplier side might be generic, unless you are talking Uber massive scale. But the demand side is much more specific and will require a custom made mobile app.