Email Heat Grids in Revenue Cycle Explorer

I'm trying to better understand the output of the email heat grids in the Revenue Cycle Explorer.

For example:

1. Email Click Activity Heat Grid: does the green box represent the most clicks on all emails sent out of Marketo to leads in the past 7 days?  Or is it referring to one email that was sent in 7 days. I'm trying to understand if the relationship of boxes is 1 to 1 or 1 to many.

2. Email Sent Activity: again are the boxes a 1 to 1 relationship?

Any insight would be great.

Thank you!

Christine