Big Data in an Ordinary Day

"Big data" describes the enormous volumes of information collected from phones, sensors, transactions and online activity, along with the tools used to find patterns in it. The phrase can sound abstract, but its effects show up in small decisions throughout an ordinary day, from what you watch to how quickly you get home. Following one typical day shows where it quietly shapes everyday choices, and where it raises real concerns.

7:00 a.m.: checking the weather

Modern weather forecasts depend on huge amounts of data: readings from satellites, weather balloons, ground stations, aircraft and ocean buoys, fed into computer models run on supercomputers. Forecasts have become steadily more accurate over the decades, and a five-day forecast today is about as reliable as a one-day forecast was in 1980, according to the US National Oceanic and Atmospheric Administration. When you decide whether to take an umbrella, you are relying on one of the oldest big data systems in the world.

8:00 a.m.: the commute

Navigation apps such as Google Maps and Waze estimate traffic by combining anonymized location and speed data from many phones on the road, along with reports from users and data from road authorities. That is how an app can suggest a faster route around an accident minutes after it happens. Cities also use traffic data to time signals and plan roadworks.

10:00 a.m.: a card payment

Each time you tap a card, banks and payment networks check the transaction against patterns of normal behavior, such as where and how you usually spend, in a fraction of a second. Transactions that look unusual can be flagged or blocked, and you may get a text asking whether a purchase was yours. These systems prevent large amounts of fraud, although they occasionally block legitimate purchases, especially when traveling.

1:00 p.m.: shopping online

Online stores recommend products based on what you and similar shoppers have viewed and bought. Retailers also use data to decide what to stock, where to place warehouses and how to set prices. Prices on some websites and for services such as rides and flights can change based on demand, a practice known as dynamic pricing.

6:00 p.m.: a workout

Fitness trackers and smartwatches record steps, heart rate and sleep. Individually, the data helps people track habits. Pooled and anonymized, data from large groups of volunteers has been used in research studies on topics such as sleep patterns and heart rhythm. The Apple Heart Study, published in 2019, involved more than 400,000 participants and looked at whether a smartwatch could identify irregular heart rhythms.

8:00 p.m.: choosing something to watch

Streaming services such as Netflix and Spotify use viewing and listening histories to recommend shows, films and songs, and to decide what content to commission. The rows on your home screen, and even the artwork shown for a title, may be tailored to your tastes.

Behind the scenes: energy and public services

Smart electricity meters help utilities balance supply and demand and plan for peak periods. Public health agencies analyze data to spot disease outbreaks, and city governments use it to plan public transport routes and respond to service requests. These uses are less visible but affect daily life just as much.

Even something as simple as an online search draws on big data: search engines rank results using signals from billions of web pages and patterns in how people search.

The concerns

Privacy: location history, purchases and browsing can reveal a great deal about a person. Data that is "anonymized" can sometimes be re-identified when combined with other information.
Data breaches: large data stores are attractive targets for hackers.
Bias: decisions based on data, such as lending, hiring or policing, can reflect and reinforce existing inequalities if the data or models are flawed.
Transparency: it is often unclear what is collected, who it is shared with and how decisions are made.

Laws such as the European Union's General Data Protection Regulation, which took effect in 2018, and the California Consumer Privacy Act give people certain rights to see, delete or limit the sale of their personal data.

Taking some control

Review app permissions, especially for location, microphone and contacts.
Check privacy settings on phones, browsers and major accounts, and turn off ad personalization if you prefer.
Clear or pause location and search histories where available.
Be selective about loyalty programs and apps that request more data than they need.

Big data makes many everyday services faster and more convenient. Understanding where it is used makes it easier to enjoy those benefits while deciding how much of your own information you are comfortable sharing.