Interesting scenarios for GPS-based False Positives & False Negatives

Owned by Diarmid Mackenzie
May 04, 2020
2 min read

What conditions need to be met for GPS logs to be a good proxy for a person’s location?

  • switched on

  • operating normally

  • with access to GPS signal

  • with the app running

  • with the phone’s owner

  • with space to store GPS data

  • fairly static (hence GPS pings every 5 mins is a good model for location)

When might these not be the case?

  • phone switched off

  • airplane mode

  • out of GPS signal

  • phone away from the phone’s owner

  • movement

  • location permissions off

  • storage permissions off

  • out of storage space

  • out of battery

  • battery saver kills app

  • app crashed

  • app did not restart when phone powered off

Let’s split the above into human factors & technical factors. Red ones are technical factors - important, but in terms of thinking about real-world scenarios they are less relevant.

In the real world, when do these things happen?

Phone switched off:

  • Theatre

  • Cinema

  • AIrplane

  • Restaurant

  • Hospital

AIrplane Mode

  • Airplanes

No GPS signal

  • Subway / Underground

  • Inside a building

  • Tunnels

  • Caves

Phone away from owner

  • Left in locker…

  • Gym

  • Sports

  • Swimming

  • Spa

  • Left at a table / with friends…

  • Dancing

  • Beach / sea

  • Lost phone

  • Lent to someone else

Movement

  • Walking

  • Cycling

  • Car

  • Taxi

  • Bus

  • Long-distance Bus

  • Tram/Trolley

  • Subway

  • Boat

  • Ferry

  • Ship

  • Plane

  • Helicopter

  • Horseback

Further assumption is that proximity of people (latitude / longitude) is a good proxy for risk of infection. What does this assume?

  • People at the same altitude

  • No barriers/walls

  • No PPE

When might these assumptions not hold?

People at the same altitude

  • Office blocks

  • Apartment blocks

  • Shopping Malls (Multi-level)

  • Department Stores

  • Bridges / wakways

  • Boardwalks / piers

  • Scaffolding

Barriers / walls

  • Office blocks

  • Apartment blocks

  • Shops

  • Changing Rooms

  • WC cubicle

  • Phone Boxes (UK style - do these even still exist anywhere?)

  • Elevator

Where are there particular risks of infections from fomites? Common objects in the environment that mutliple people may touch - ideally we would increase our sensitivity to collocation (even at some distance in time) in the locations of these objects.

  • ATM

  • Pedestrian crossing

  • PIN pad on payment system

  • Door handles

  • Counter-tops

  • Goods in shops

  • Crockery, cutlery, glassware in resaturants, cafes, bars.

  • Shopping carts

  • Chairs

  • Tables

  • Benches

  • Theatre / Cinema seats

  • Bus Stops

  • Handrails

  • Vending machines

  • Ticket machines

  • Windows on Public Transit

  • Fruit machines

  • Arcade machines

  • Table football

  • Bowling balls

  • Public pianos

  • (and I’m sure. many more…)

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