Google already monitors your online shopping - but now it wants to work with payment firms to monitor what you buy offline as well.

The search giant says it has access to roughly 70 percent of U.S. credit and debit card transactions through partnerships with other companies that track that data.

Now it hopes to use this to tell advertisers when their online ads have led to an offline purchase.

Google is keeping an eye on what you're buying offline in addition to monitoring your online shopping in its latest attempt to sell more digital advertising. The offline tracking of most credit and debit card transactions will help Google to automatically inform merchants when digital ads appearing on its vast marketing network translate into sales at a brick-and-mortar store. Google plans to unveil the store-sales measurement tool Tuesday, May 23, 2017, in San Francisco at an annual conference it hosts for its advertisers.

HOW IT WORKS Google's computers are connecting the dots between what people look at after clicking on an online ad and then what they purchase with their credit and debit cards. For instance, if someone searching for a pair of running shoes online clicked on an ad from a sporting goods store but didn't buy anything, an advertiser might initially conclude that the ad was a waste of money. But Google says its new tool will now be able to tell if the same person bought the shoes a few days later at one of the advertiser's brick-and-mortar stores. Advertisement

Google believes the data will show a cause-and-effect relationship between online ads and offline sales.

'Machine learning is key to measuring the consumer journeys that now span multiple devices and channels across both the digital and physical worlds,' it said.

If it works, that could help persuade merchants to boost their digital marketing budgets.

The Mountain View, California, company already runs the world's biggest online ad network, one that raked in $79 billion in revenue last year.

That puts it in the best position to capture any additional marketing dollars spent on computers and mobile devices.

Google executives told The Washington Post they are using complex, patent-pending mathematical formulas to protect the privacy of consumers in the scheme.

The mathematical formulas convert people's names and other personal information into anonymous strings of numbers.

The formulas make it impossible for Google to know the identity of the real-world shoppers, and for the retailers to know the identities of Google's users, Google says.

The companies know only that a match has been made, and Google does not get a detailed description of the individual transactions, just the amount spent.

'Through a mathematical property we can do double-blind matching between their data and our data,' said Jerry Dischler, vice president of product management for AdWords, in an interview with The Washington Post.

'Neither gets to the see the encrypted data that the other side brings.'

Dischler said the scheme was a 'revolutionary' step forward for both Google and advertisers.

Google unveiled the store-sales measurement tool Tuesday in San Francisco at an annual conference it hosts for its advertisers.

However, Google would not say how merchants had obtained consent from consumers to pass along their credit card information, simply saying 'you can measure store sales by taking advantage of Google's third-party partnerships, which capture approximately 70% of credit and debit card transactions in the United States.

'There is no time-consuming setup or costly integrations required on your end.

'You also don't need to share any customer information. After you opt in, we can automatically report on your store sales in AdWords.

In the past, both Google and Facebook have used purchase data for a limited set of consumers via loyalty programs.

Google will also use AI to enable better location ads.

'In-market audiences uses the power of machine learning to better understand purchase intent,' it said.

Google says it has access to roughly 70 percent of U.S. credit and debit card transactions through partnerships with other companies that track that data.

'It analyzes trillions of search queries and activity across millions of websites to help figure out when people are close to buying and surface ads that will be more relevant and interesting to them .

'For example, if you're a car dealership, you can increase your reach among users who have already searched for 'SUVs with best gas mileage' and 'spacious SUVs''

The gathering gives Google a prime opportunity to woo advertisers - one that it surely welcomes, given that it's still trying to overcome a marketing boycott of its YouTube video site .

The boycott began two months ago over concerns that Google hadn't prevented major brand advertising from appearing alongside extremist video clips promoting hate and violence.

Google is also introducing several other features designed to help merchants drive more traffic to their physical stores and to gain a better understanding on how digital ads appearing across a variety of devices are affecting their sales.

Most of the new analytics twists draw upon Google's inroads in 'machine learning' - a way of 'training' computers to behave more like humans - to interpret the data.

HOW TO OPT OUT Google gives its users the option to limit the company's tracking and control what types of ads they are shown. Google says its computers can collect identifying data triggered by online clicks and match it with other identifying information compiled by merchants and the issuers of credit and debit cards to figure out when a digital ad contributes to an offline purchase. Shoppers remain anonymous, meaning they aren't identified by their names, according to Google. And the company says it doesn't share any of its anonymized information with its advertisers; instead, it targets ads at individuals who fit demographic profiles sought by advertisers. Advertisement

Google's search engine and Chrome web browser are a rich source of data about people's interests and online activities that it can feed into machine-learning systems.

In the case of the store sales measure tool, Google's computers are connecting the dots between what people look at after clicking on an online ad and then what they purchase with their credit and debit cards.

For instance, if someone searching for a pair of running shoes online clicked on an ad from a sporting goods store but didn't buy anything, an advertiser might initially conclude that the ad was a waste of money.

But Google says its new tool will now be able to tell if the same person bought the shoes a few days later at one of the advertiser's brick-and-mortar stores.

Google says it has access to roughly 70 percent of U.S. credit and debit card transactions through partnerships with other companies that track that data.

That means Google still won't be able to document every purchase made using plastic - and it still has no way of knowing when people buy something with cash.

The digital dossiers that Google has compiled on the more than one billion people who use its search engine and other services, including Gmail, YouTube and Android, worry privacy watchdogs.

Google gives its users the option to limit the company's tracking and control what types of ads they are shown.

Google says its computers can collect identifying data triggered by online clicks and match it with other identifying information compiled by merchants and the issuers of credit and debit cards to figure out when a digital ad contributes to an offline purchase.

Shoppers remain anonymous, meaning they aren't identified by their names, according to Google.

And the company says it doesn't share any of its anonymized information with its advertisers; instead, it targets ads at individuals who fit demographic profiles sought by advertisers.