Although Nielsen already offers tools to help track when consumers buy products in-store after seeing online ads, the measurements company has inked an agreement with Foursquare to create an improved product. Location data company Foursquare will offer information which, combined with Nielsen’s marketing tools, will offer a more complete picture of consumer activity. The new capabilities will come at a price. Nielsen digital measurement clients will be required to buy into the version with Foursquare data included.

The Wall Street Journal notes that current Nielsen clients who pay the extra fee will have access to “a standalone dashboard through which they can access the information, as well as ‘insights’ from Foursquare analysts.”

“For certain sets of clients looking to drive in-store purchases we’ve heard a need to better understand who’s turning up on-site,” said Nielsen managing director of digital Andrew Feigenson.

Foursquare will collect data from “a panel of 1 million people in the U.S. who use its consumer-facing location-based products, including Foursquare and Swarm,” and have agreed to participate anonymously.

“The vast majority of consumer spending happens offline,” said Foursquare chief executive Jeff Glueck. “Digital marketers have all these data advantages, but if you run Subway stores or grocery stores it’s hard to know as a marketer which ads are working. In our case we understand because we are on the phone when the phone is actually stopping at the Starbucks or the J. Crew store.”

Glueck adds that another advantage of such “foot traffic” data is that it’s available on a daily basis, “whereas sales data can take weeks or even months to collect and parse.” Such daily store visit data “may therefore enable marketers to be more nimble with making adjustments to their marketing activity.” Foursquare offers its own measurement tool Attribution by Foursquare, and ad targeting solution Pinpoint separate from the Nielsen deal.

Nielsen and Foursquare aren’t alone in offering solutions to better understand the impact of online ads on real-world behavior. Facebook, Google, comScore and others tout similar tools aimed at marketers.