
Private location trace intersection feed
Ideally, we want platforms that achieve sustainability and longer-term value by increasing real-world
community connections, trust, capacity for collective action (known as bonding social capital), as
well the number of trusted links to people in other communities (known as bridging capital). At its
core, your feed should be representative of people that matter to you.
The physical spaces we navigate are strong determinants of many aspects of our lives and values,
from our wellbeing [
4
] to our choice of collaborators [
5
] and the opportunities for economic growth
we’re exposed to [
6
]. Location history is a better predictor of your interests than the demographics
used by current matching apps (e.g., dating app, content recommendation, etc.) [
7
], and is strongly
predictive of which friendships you already have [8]. Leveraging GPS location data in social media
has a long history demonstrating its value, but has been a series of privacy nightmares that require the
sharing of this location data to a third party, often to be stored indefinitely and monetized without any
visibility or accountability to the user.
We propose a new approach to building social media feeds that are optimized for social capital
building via private matching over location histories, where friends are shown in proportion to their
potential to build new within-community relationships and to reinforce community social capital,
requiring no third-party interactions or capture of data.
All data sharing is done securely such that no parties ever see anyone else’s location data, and only
each pair of users can see the size of the location data overlap between them.
This approach is naturally extensible to a huge range of similar matching approaches ranging from
shared photo matching, or shared friendship matching (including from existing social networks), to
simple interest matching, all without needing trusted third parties or the exposure of any personal
information. In doing so, this creates an in-built incentive for users to make personal data accessible
(in an encrypted and private manner) to ensure they appear on others’ feeds and can participate in the
social ecosystem.
In summary, this paper:
•
Presents a novel approach to building a social feed that represents real social relationships
via calculations of set intersections between pairs of individuals without the need for a third
party or transmission of any unencrypted data, ensuring no escape of any private information
to anyone.
• Validates the value of location trace based matching as a measure of friendship on existing
data using two different computational examinations, in turn motivating its use in building a
feed optimized for social capital building.
•
Prototypes the approach with a reference implementation and demo app to show that this
can be done with extremely low computational cost.
•
Proposes and discusses the extensibility of this private set intersection driven feed paradigm
to other personal datasets and explores how this creates new social incentives around private
data sharing for matching.
A longer, more verbose version of this publication with additional figures will be made available
online via pre-print servers due to page limits.
2 A social recommendation algorithm
For two friends Alice & Bob, the rate at which content is shown on a feed should be proportional to
the physical-world relevancy of their ties (here the likelihood they’ll be at the same location).
When Bob friends Alice, Bob can make a request to Alice to begin a multistep private set intersection
on the mobility traces (location history) of both Bob and Alice. To make matching on this information
easier, Alice can provide each point in her GPS trace,
Tr
A
, as a geohash [
9
] at an arbitrary resolution,
r.
Geohash converts GPS coordinates to strings at a varying length of string to provide an arbitration
resolution. For example, one can know that a GPS coordinate is inside the MIT Media Lab building
using the string ‘
drt2yr7x
’. If Alice desires, she can allow others to match on extremely detailed
location traces by using a high-resolution geohash in the form of a long string (
r= 8
characters). Or,
2