Data Storytelling and Data Viz Approach
For this week's viz, I wanted to focus on the differences of the metrics across vehicle classes as well as across time. To look at the differences across vehicle types, I used the new step line capability of Tableau 2018.1, using color to delineate between the different vehicles.
I used a few different methods to look at the differences over time. The step line definitely shows changes across the years, but I also wanted to see how decades compared to the full time period. I limited my data to 1950 to 2009, added some parameter controls and calculated fields to account for some decade logic, and them employed these in the vizzes. The main step line viz filters down to the selected decade, while a summary step line viz highlights the selected decade, while lowlighting the other decades. I achieved this with a dual axis chart - the primary axis being my metric as a step line, and the secondary being a constant with an area chart as the mark type.
At the bottom of the dashboard, I used a shape viz to drive interactivity and filter two sets of BANs - one for the selected decade, and the other for the entire time period. This allows the user to clearly see how the minimum, maximum and average metrics for the selected decade compares to the full time period.
There are a few notes on the data this week:
- Light Duty Vehicles, Short Wheelbase: Until 2006, this data is for passenger cars, and includes motorcycles through 1989. From 2007, this class includes passenger cars, light trucks, vans, and SUVs with a wheelbase less than or equal to 121 inches.
- Light Duty Vehicles, Long Wheelbase: From 1949 through 1965, these figures were included in the Heavy Duty Trucks category. Until 2006, this data includes all vans, pickup trucks, and SUVs with 2 axles and 4 tires. From 2007, this category includes large passenger cars, pickup trucks, vans and SUVs with a wheelbase greater than 121 inches.
- Heavy Duty Trucks: Until 2006, this data includes single unit trucks, with 2 axles and 6 or more tires, and combination trucks. From 2007, the data includes trucks with 2 axles and 6 or more tires with a gross vehicle weight of more than 10,000 pounds.
- All Motor Vehicles: For the entire period, includes busses. From 1989, includes motorcycles. These figures are not otherwise accounted for in the other categories.
This week's data source comes from the United States Energy Information Administration, or the EIA.