A Marimekko chart (a "mekko", or market map) shows two things at once. Each column's width is the size of a segment; each block's height is a player's share within that segment. A block's area is that player's sales in that segment.
Consultants use it to show where a client is strong and whether those segments matter. Tools such as think-cell build them in PowerPoint; here you learn to read them.
The trap: a tall block in a thin column is a big share of a small market. To get dollars, multiply share by segment size. To get a player's share of the whole market, add its dollars across segments and divide by the total, not average its shares.