A new Nielsen targeting product aims to let advertisers buy online audiences based on their TV consumption patterns. It’s an extension of what the measurement firm has already done linking CPG purchase data to online media, and another mile marker on Nielsen’s road map for a digital media marketplace geared to the needs of broadcast media planners. To build the data segments, Nielsen takes a representative subset of its online and TV panelists, observes how they behave across TV and the web, and extrapolates that to a larger audience. Those segments consist of things like shows most viewed, channels most viewed, light or heavy TV watchers, and genres. The segments can be accessed in a few ways, including through an API, a direct…