The increasing popularity of smartphones has enabled a new class of SNS, de- signed around the purpose of sharing location data with one’s social network. Zheng defines location-based social networks (LBSNs) as a form of social net- work site, where people can record their current location, and accumulate a profile of historic location records. These are distinguished from SNSs which may add location-based elements, as the context and purpose of the system is defined by the dependency on generating and sharing location data [146].
These services build on the work of early location-based services (LBSs), which used self-reported locations or GSM localisation on mobile phones to deliver simple services over standard cellular technologies such as Wireless Application Protocol (WAP) or Short Message Service (SMS), such as recom- mendations for nearby points of interest [133], marketers sending location- appropriate adverts by SMS [4], or the ability to send messages to physically co-located peers. In recent years, encouraged by the growth of the smart- phone market, LBSs have increased in sophistication, taking advantage of the improved location-sensing capabilities of phones equipped with GPS receiv- ers, and the availability of higher-bandwidth cellular Internet connections to provide richer services such as high-resolution mapping with turn-by-turn directions and real-time road closure and traffic incident alerts, and the ability to share one’s location with their peers via an existing SNS or one managed by the LBS provider [129].
LBSNs involve the sharing of location data between peers. Tang et al. con- sider such sharing to either be purpose-driven, where people choose to share their location to achieve a utilitarian purpose such as coordinating a meeting,
Figure 2.5:Screenshot of the cashback service Quidco that incentivises checking-in with commercial partners and sharing this with one’s social network.
or social-driven, where people choose to share their location as an act of im- pression management, and not because the information is necessarily useful to someone else [126]. In recent years, a number of prominent social-driven LBSNs have emerged, such as Foursquare,3 which allows a user to “check-in” to a place of interest they are currently visiting, and share this with their peers on the service, or to a third-party SNS such as Facebook. As well as differ- ent motivations for disclosures, the frequency of location-sharing often varies between these two forms. In purpose-driven services such as Apple’s Find My Friends, a user’s location is tracked continuously and made available to a sub- set of peers, while social-driven services often rely on users making discrete check-ins [142].
In recent years, the operators of LBSNs have looked for ways to make rev- enue from their services, which are usually provided for free. As with many other online enterprises, this has often meant incorporating advertising into
their services, and the commercialisation of their users’ data. The current loc- ation of users is a rich commodity, which had been acknowledged long before such services became commonplace [133]. Using demographic data disclosed by users or drawn from their online presence, advertisers are able to reach highly- targeted groups of people when they are located in a commercially useful area. The perceived value of such services to its users might come from the ability to offer context-specific discounts. Some LBSNs later partnered with advertisers to offer discounts if a user checks-in to a specific business, thus making the user a complicit advertising agent by promoting the brand to their social net- work for compensation. Foursquare employed a gamification element which crowned users the “mayor” of a particular location if they checked in there the most. In 2010, Foursquare partnered with Starbucks to offer coupons to users who became mayor of a Starbucks outlet [118], a direct form of compensation for users who promoted the brand to their social network. Other examples in- clude sending text messages to people who are near a particular business [89], and electronics retailer Radioshack’s partnering with Foursquare to offer dis- counts to users who achieved a certain number of “badges” by checking in to a set of locations [110]. While these developments augment existing LBSNs with commercial elements, there have also been applications which are built around an entirely commercial premise. Quidco4 is an online cashback provider, who developed a mobile application where users could see a list of nearby businesses and check-in for a small cash incentive or coupon at a retailer, or receive an additional incentive if this check-in was shared with the user’s social network, as shown in Figure 2.5. In addition, Quidco shares user data with its partners when providing this service.5 We term these new systemsincentivised location sharingservices.
4Quidco: http://www.quidco.com/
Privacy challenges
The ability to share one’s location builds a historic record of a person’s mo- bility, constituting a particularly sensitive aspect of context. Over-exposure of someone’s current or historic locations can risk revealing their home address or mobility patterns to an unknown adversary.
Previous work has shown that the users of LBSNs primarily exhibit concern about the context in which someone is making a request for their location, and to a lesser extent, what the purpose of the request is [74]. Barkhuus and Dey found that services which employed continuous tracking by other people induced greater concern than services which detected location for the direct delivery of a service to the user, because of the lack of perceived utility for the person being tracked [3]. Similar concerns were articulated by participants in a user study by Consolvo et al., where location-sharing services which allowed others to request one’s location felt “creepy” and could affect relationships with those making inappropriate requests [18].
As with other SNSs, the trustworthiness of LBSNs is a significant concern. Tsai et al.’s survey of LBSNs found that a third of services did not have a privacy policy to explain how users’ data would be processed [131], and that the major- ity of services which did have policies retained permissions to store personally- identifiable information (PII) indefinitely, which includes any data which can be used to uniquely distinguish an individual [86]. The context-dependent sens- itivity of location disclosures places great responsibility on the user to manage the interfaces used to control who can view check-ins. The authors also noted that while three-quarters of services expose some privacy controls, these are often not made obvious to users.
While much of the research concerning privacy risks of LBSNs have focused on whether the service provider can be trusted, and the social implications of over-sharing with one’s peers, some services are explicitly designed to expose one’s location to strangers, with potentially more damaging consequences. The
service Grindr is popular with men who have sex with men to discover and talk to others who are nearby. Fiebig et al. found significant security shortcomings which allowed user profiles and social networks to be exposed by fabricating requests to the service [29], while a report by Synack researchers found that the exact location of users could be identified through trilateration when making spoof requests [125]. This has implications in cultures where people may not be able to be forthcoming about their sexual identity and could be the subject of abuse or implicated criminally, with Toch and Levi noting that harassment of users of such services was not uncommon [130].
Concerns with LBSNs that employ mobile advertising have been identified. King and Jessen note that data protection regulation in the EU and US have gaps which could lead to abuses of behavioural advertising, specifically citing the lack of consent being sought before collecting or using personal data, surveillance of people’s behaviour, and unwanted solicitation of commercial activity [67]. This is of particular concern considering the sensitivity of data being collected and shared between partners. Consent is found to be an important feature in acceptance of mobile advertising, with Scharl et al. observing that the intrus- iveness of mobile advertising is liable to being perceived as spam if people do not feel in control of what they receive [112]. Similarly, Xu and Teo’s theoretical study of privacy concerns in such applications found that the perceived benefit, particularly if the implementation of advertising was considered entertaining, was a significant predictor of people’s acceptance of having advertisements tar- geted to them [145].
In this section, we have introduced some instantiations of social network sites and location-based social networks. The novelty of these services, and the blending roles between them, has significant implications for how people consider and use these services.
In the next section, we consider the challenges posed by attempts to research these services from ethical and privacy perspectives.