After the United Kingdom 2017 General Election, on Thursday 8th June 2017, I had many conservations about our First Past The Post system (FPTP), and why we do not have a Proportional Representation (PR). In the UK FPTP system, we have 650 individual battlegrounds, each representing one seat, the party with the most seats wins. This means that a party could technically score second place in every battle but have zero seats in Parliament.

In this tutorial, we will walk through the creation of Double-Spaces Doughnut charts in Tableau.

Disclaimer: This tutorial goes through several techniques which will hopefully help you in your journey. However, and as always, try to find the most appropriate visualisation for specific data visualisation and dashboard requirements.

## Data

Note: We have two records per segment as we are going to use data densification to give us additional points for drawing.

## Calculated Fields

With our data set loaded into Tableau, we are going to create the following Calculated Fields and Bins:

Path (bin)

• Right click on Path, go to Create and select Bins…
• In the Edit Bins dialogue window:
• Set New field name to Path (bin)
• Set Size of bins to 1
• Click Ok

Zero

`0`

Index

`INDEX()`

Seat Share

`MAX(IF([Type]="Percentage of Seats") THEN [Values] END)`

Vote Share

`MAX(IF([Type]="Percentage of Votes") THEN [Values] END)`

TC_Position

`WINDOW_MAX(MAX([Position]))`

TC_Values

`WINDOW_MAX(MAX([Values]))`

X

`SIN([Index]*2*PI()/180)*[TC_Position]`

Note: We need to convert percentages to Radians by multiplying by PI() and then dividing by 180.

Y

`COS([Index]*2*PI()/180)*[TC_Position]`

Color

`IF [Index]*2/360 <= [TC_Values] THEN WINDOW_MAX(MAX([Party])) ELSE "Gray" END`

So now that we have created a lot of Calculated fields, we will now put this together into a Worksheet.

## Worksheet

We will now build our worksheet by:

• Drag Type onto the Details Mark
• Drag Path (Bin) onto the Columns
• Right click on Path (Bin) and check Show Missing Values
• Drag Path (Bin) onto the Detail Mark
• Drag Party onto the Details Mark
• Drag Party onto Columns
• Change the Mark Type to Line
• Drag Position onto Path
• Right click on Position and choose Dimension
• Drag X onto Columns
• Right click on X, go to Compute Using, select Path (Bin)
• Drag Y onto Rows
• Right click on Y, go to Compute Using, select Path (Bin)
• Drag Color onto the Color Mark
• Right click on Color, go to Compute Using, select Path (Bin)

After this you should have the following:

We will now complete the visualisation by adding the central text.

• Drag Zero onto Rows
• Right-click and select Dual Axis
• Right-click on the axis bar and select Synchronize Axis
• You should have SUM(Zero) as an option on Marks, now
• Remove all objects
• Change the Marks to Text
• Drag Vote Share to Text
• Drag Seat Share to Text
• Right Click on Seat Share and Vote Share and change the Number format to 1 decimal place percentage
• Go to the Y object in Marks and removes the Measure Names; this has been added automatically.

We should now see the following:

You have now built a worksheet that shows a Double-Spaced Doughnut Chart where the inner circle represents the number of votes and the outer circle represents the number of seats.

We will now do the following to get the look that we require:

• Remove all Grid Lines
• Edit the party Color
• Remove the Tooltips on for the Doughnut