SAN FRANCISCO (AP) — Google already monitors your online shopping — but now it's also keeping an eye on what you're buying in real-world stores as part of its latest effort to sell more digital advertising.

The offline tracking scans most credit and debit card transactions to help Google automatically inform merchants when their digital ads translate into sales at a brick-and-mortar store.

Google believes the data will show a cause-and-effect relationship between online ads and offline sales. If it works, that could help persuade merchants to boost their digital marketing budgets.

GOOGLE WINDFALL

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

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.

SMARTER AD TRACKING

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. 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.

DIGITAL DOSSIERS

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.