By filtering the left column, you will see the corresponding traffic results in the right column.
In the Platform-Wide Data ,you can see
the corresponding traffic total.
In the Placement-Specific Data, you will see details of each app/site and seller.
Click on each column in the right , you will see the detail traffic information.
You can see the traffic through the map, the color darker,the traffic greater.
Click on "banner".Check details of sellers and App/Site for banner traffic.
You can also check which inventory gets the most traffic in your targeted Geo and which banner size gets the most traffic.
This is an example for US iOS banner traffic.