Data Visualization - Tableau

Data types

• In Tableau, a Dimension (listed at the top of the Data window) is a categorical variable, including text variables, date variables, geographic location names, and discrete numerical variables. 
• A Measure is a continuous numerical variable, which includes geographic coordinates.

Data structure

• Tableau expects a very particular structure for the data you import.
• In some programs this is called a "tall" or "narrow" format, rather than a "wide" format that is occasionally distributed by data producers.
• There are a variety of tools that can be used to reshape (or unpivot) data in this fashion, including the Tableau Excel Add-in.
• The plug-in is only available for Windows; Mac users can use a PivotTable feature to replicate this.
• Tableau also allows you to join multiple tables together to merge and blend data.

Selecting the file

1. Open Tableau
2. Click the “Open Data” button
3. Select “Microsoft Excel”
4. Select the “hurricane_tracts.xlsx” file
5. Drag “hurricane_tracts” over Drag sheets here

Fix variable type errors

1. For “Season”, change variable type to String*
2. For “ISO time”, change variable type to Date & time

*In Tableau, dates need a month and day, so a year is not a date. If your data are annual, you can add a fake month and day that you later ignore.

Finalize import

1. Click “Go to Worksheet”
2. Move “Season (Count)” from Measures to Dimensions

Option A: Building a line chart manually, with drag-and-drop

• Drag “ISO time” to Columns or top of view area
  • The default aggregation when you do this should be "Year(ISO time)" in blue, as shown below. 
  • If you get something else, just use the arrow on the right of the ISO time bubble and find the first "Year" in the drop down.
• Drag “Number of Records” to Rows or left of view area

Limit to last 20 years

• Drag “ISO time” to Filters
• Click “Relative dates”
• Select “Years”
• Click the button for “Last”
• Adjust to 20 years

Option B: Create a line chart with Show Me

• Click “ISO time”
  • The default aggregation when you do this should be "Year(ISO time)" in green, as shown below. 
  • If you get something else, just use the arrow on the right of the ISO time bubble and find the second "Year" in the drop down.
• Ctrl-click “Number of Records”
• Open Show Me
• Select line chart

Why are the two charts so different?

• One has “Year(ISO time)” in green, while the other has it in blue. 
• In the data window, “ISO time” is blue, which means “discrete.”
• A discrete variable is like a category; values may have an order, but there isn’t anything in between them.
• Line charts normally use a “continuous” date, though, so Show Me converted “ISO time” to green.
• A continuous variable is like the full number range; you may only have a few values, but there are more possible numbers in between them.
• If you click the "+" sign to expand the Year variables in each chart, they will both disaggregate down to the Quarter level.  The "discrete" chart, however, will treat quarters as categories, whereas the "continuous" chart will just add more points to the line.

New in Tableau 8.2: Building a Box-and-whisker Plot

• Drag “ISO time” to Columns
• Drag “Wind in knots” to Rows
• Change “Wind in knots” to use Average instead of Sum
• Drag “Name” to Detail
• On Show Me, click on " Box-and-whisker plot"
• Limit to last 20 years (see Line chart demo)

Mapping Hurricane Tracts

• Double-click “Latitude” and “Longitude”
• Change both to Dimension
• Drag “Serial Num” to Detail
• Change mark type to Line
• Drag “ISO time” to Path
• Change “ISO time” to Continuous, Hour
• Optional: Drag “Wind in knots” to Size

More information available on Tableau's Path Shelf

Animating the tracts

• Double-click “Latitude” and “Longitude”
• Change both to Dimension
• Drag “ISO time” to Filters
• Click on Years (discrete) and select 2005 only
• Drag “ISO time” to Pages
• Click “Add all members”
• Change the Pages version of “ISO time” to Continuous, Hour
• Drag “Name” to Label
• Under Pages, click “Show History” and change settings to pick “All” marks
• Click the play button and speed up the animation

Create a new dashboard

1. Click the new dashboard button at the bottom
2. Drag the unfiltered map to canvas
3. Drag the box and whisker plot to the bottom of the canvas
4. Click the arrow at the upper right of the box and whisker to select “Use as Filter”
5. Click a year name or range to change the map

Saving to the Web

1. Hide any sheets you don’t want visible
2. Click the “save” icon
3. Log into your Tableau Public account (or create one)
4. Choose a name for your workbook
5. Decide if you want to show visible sheets as tabs
6. Click Save
7. Click “Open in Browser Window”
8. Use Export button at bottom to get Image or PDF

This guide has been adapted using "Tableau Public: Tutorial" by Duke University Libraries.