Disclosed example audience measurement apparatus include first estimator means for determining a first audience metric based on set-top box return path tuning data obtained from a plurality of set-top boxes located in a first geographic area, second estimator means for determining a second audience metric from a portion of audience measurement data corresponding to a second geographic area different from the first geographic area, the portion of the audience measurement data associated with monitored sites in the second geographic area having second set-top box characteristics that correspond with first set-top box characteristics of the plurality of set-top boxes located in the first geographic area, and third estimator means for (i) determining a ratio of the first audience metric to the second audience metric, and (ii) processing the audience measurement data based on the ratio to determine an audience exposure metric estimating exposure to media in the first geographic area.