Methods and apparatus to monitor media content at a content display site are described. An example method includes assigning a first set of weights to each of a plurality of panelists based on a set of collected characteristics for each person of a subset of unmeasured persons at unmeasured locations, the subset of unmeasured persons being the unmeasured person for which the collected characteristics are known, selecting a subset of the panelists based on the first set of weights, each panelist of the subset of panelists selected to be representative of an unmeasured person of the unmeasured persons, re-weighting the subset of the panelists based on estimated characteristics of the unmeasured persons at the unmeasured locations to generate a second set of weights, generating a virtual panel including measurement data collected for the subset of the panelists as virtual panelists, the measurement data of the virtual panel representing the media consumption activity of the unmeasured persons at the unmeasured locations, and scaling the measurement data of the virtual panel collected from the subset of the panelists to estimate media consumption at the unmeasured locations.