Each colored dot displayed on the chart approximates a one-degree cell (60 minutes of latitude by 60 minutes of longitude) and is referred to as a "cell" in the legend below.
Monthly density plot totals:
| Red Cells: The monthly plot totaled over 50 vessels | |
| Orange Cells: The monthly plot totaled between 15 and 49 vessels | |
| Green Cells: The monthly plot totaled between 5 and 14 vessels | |
| Blue Cells: The monthly plot totaled 4 or fewer vessels | |
| Empty Cells: No vessels |