Title: Location Data
Description: Most of the modern online economy is based on websites offering free services and content in exchange for advertising access and user data. Web companies collect vast troves of data about their users in order to better target their advertisements. An important subset of this harvested data is the locations visited by users. Location data is valuable as it is a ``real world" signal compared to online behaviors: a visit to a store is a stronger signal than a visit to a website, and location data can reveal user attributes that are interesting to advertisers. The collection of this data, however, raises many concerns. Location data can reveal important attributes that users may not wish to disclose: ZIP codes can reveal income and race, visits to places of worship may allow discrimination, and insurers may want to know about trips to hospitals. The risks exist at both an individual level, with location tied to physical safety, and at a collective level, with inference about group membership a necessary step towards discrimination.

In this thesis, I examine issues of privacy and fairness in the use of location data. In the first portion, I empirically demonstrate new attacks on the anonymity and privacy of users, including a theoretical basis for user identification. In the second portion, I propose and analyze new solutions for dealing with privacy, anonymity, and fairness in the collection and use of location data. In contrast to previous work which presents privacy in abstract ways or ignores the power of data aggregators, the work presented here focuses on concretely informing users and incorporates the economic incentives driving privacy and fairness concerns.