Market Share metrics are normalized metrics produced on a monthly basis measured at the category level which can be compared as market shares to sites within the category

With the exception of Unique Visitors, all the metrics can be "summed" to produce a market share metric. Unique Visitors are "uniqued" across the category, so while a comparison can be made between the number of UVs to a category and a constituent site, market share across multiple sites cannot be computed

By selecting "% Share" for the "Graph Data Type", Market Share metrics (Page Views, Visits, Total Time, and Attention) will be graphed as a stacked area, with the percentages equaling a share of the total category (which is not graphed).