it asks: How much location data must a marketer acquire before a correlation attack can de-anonymize the data?, answering through the Shannon-theoretic concept of “unicity” distance and recommending ground rules for development of truly anonymous LBS.

technology of Place

Cellular telephony has always been a
surveillance technology. As discussed
by the author, 27 cellular networks are
designed to track a phone’s location so
incoming calls are routed to the most
appropriate cell tower, usually the one
closest to the user. As most users are
aware, recent generations of cellphones
are capable of much more fine-grain lo-
cation resolution. The first step toward
adding this capability came with E911,
the Federal Communications Commis-
sion’s 1996 effort to enhance location
resolution for cellular 911 calls.b E911
established a requirement that cellular
service providers send location infor-
mation to the Public Safety Answering
Point when subscribers make 911 calls
with their cellphones. The intuition
underlying E911 was clear: It would be
desirable for emergency services to be
able to locate a victim without search-
b Notice of Proposed Rulemaking, Docket 94-
102, adopted as an official report and order,
June 1996; 12 the order and all its subsequent in-
carnations are referred to as E911 in this article.

ing the entire coverage area of a cell site. However, the technological and sociological impact has far outstripped this intuition over the past 16+ years.

One of the more immediate consequences of E911 is that many cellular handsets now have some form of GPS capability, whether standalone or network-assisted. 29 With it, service providers increasingly recognize that a much broader (and more lucrative) range of location-based services could be provided. However, it should be understood that GPS was not designed with cellphones in mind.c GPS c It was designed with guided missiles and bombers in mind. 16