I was challenged a few years back to draw an interactive Venn Diagram, not just have two transparent circles, which is not too difficult, but having two circles as well as the overlap all being selectable. As you can imagine, the mathematics is going to be quite difficult, but we will go through the steps to drawing out this visualization in Tableau.

*Note: As always never choose a data visualisation type and try to fit your data into it, instead, understand your data and choose the best visualization for your data consumers. *

## Data

Load the following data into Tableau Desktop / Public.

Category | Path |

A | 1 |

A | 361 |

B | 1 |

B | 361 |

AnB | 1 |

AnB | 361 |

*Note: we need two records for each stage as we are going to be drawing polygons and using densification to get more points on our canvas.*

## Calculated Fields

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

**P_Overlap**

- Go to
**Create Parameter**. - In
**Data type**select**Integer**. - In
**Allowable values**select**List**and enter the following values:- Add a
**Value**of**50**and**Display as**to**Small**. - Add a
**Value**of**45**and**Display as**to**Medium**. - Add a
**Value**of**40**and**Display as**to**Large**. - Add a
**Value**of**35**and**Display as**to**Maximum**.

- Add a
- Set the
**Current value**to**Medium**.

*Note: We will use this parameter to control the amount of overlap between our two circles.*

**Path (Bins)**

- Right click on
**Path**, go to**Create**and select**Binsâ€¦** - In the Edit Bins dialogue window:
- Set
**New field name**to**Path (bin).** - Set
**Size of bins**to**1.** - Click
**Ok.**

- Set

**Index**

`INDEX()-1`

**Zero**

`0`

**TC_Category**

`WINDOW_MAX(MAX([Category]))`

**TC_Circle Distance from Center**

`WINDOW_MAX(SIN([P_Overlap]*PI()/180))`

**X**

```
IF [TC_Category] = "A" THEN
IF [P_Overlap] <= [Index] AND [Index] < (180-[P_Overlap]) THEN
2*SIN([P_Overlap]*PI()/180)- SIN([Index]*PI()/180) - [TC_Circle Distance from Center]
ELSE
SIN([Index]*PI()/180) - [TC_Circle Distance from Center]
END
ELSEIF [TC_Category] = "B" THEN
IF [P_Overlap] <= [Index] AND [Index] < (180-[P_Overlap]) THEN
(2*SIN([P_Overlap]*PI()/180)- SIN([Index]*PI()/180) - [TC_Circle Distance from Center]) * -1
ELSE
(SIN([Index]*PI()/180) - [TC_Circle Distance from Center]) * -1
END
ELSE
IF [P_Overlap] <= [Index] AND [Index] < (180-[P_Overlap]) THEN
SIN([Index]*PI()/180)-SIN([P_Overlap]*PI()/180)
ELSEIF (180+[P_Overlap]) <= [Index] AND [Index] < (360-[P_Overlap]) THEN
SIN([Index]*PI()/180)+SIN([P_Overlap]*PI()/180)
ELSE
0
END
END
```

**Y**

```
IF [TC_Category] = "AnB" THEN
IF [Index] < [P_Overlap] THEN
COS([P_Overlap]*PI()/180)
ELSEIF [Index] > (360-[P_Overlap]) THEN
COS((360-[P_Overlap])*PI()/180)
ELSEIF [Index] > (180-[P_Overlap]) AND [Index] < (180+[P_Overlap]) THEN
COS((180-[P_Overlap])*PI()/180)
ELSE
COS([Index]*PI()/180)
END
ELSE
COS([Index]*PI()/180)
END
```

Suffice to say, what we are doing with the X and Y Calculated fields looks quite crazy, however:

- We are finding the point where we bend the circle in as opposed to being completed. This is based on the P_Outer parameter and how we are drawing our outer circle components.
- We have individual logical to draw the A, A and
AnB parts of our Venn Diagram.

I would suggest going through each line to try and understand what is going on here. But using these created Calculated Fields, we are now going to build our Worksheet.

## Worksheet

We are going to start building our Worksheet:

- Change the
**Mark Type**to**Polygon**. - Drag
**Category**onto**Color**. - Drag
**Path (Bins)**onto**Rows**.- Right-click on the object and ensure that
**Show Missing Values**is checked. - Once confirmed or checked, drag this object onto
**Path**.

- Right-click on the object and ensure that
- Drag
**X**onto**Columns**.- Right-click on the object, go to
**Compute****Using**and select**Path (Bins)**.

- Right-click on the object, go to
- Drag Y onto
**Rows**.- Right-click on the object, go to
**Compute****Using**and select**Path (Bins)**.

- Right-click on the object, go to

You should now see something like the following:

All that hard work creating the Calculated Fields to make sure our Worksheet is simple, well sort of, but we are not finished yet.

- Drag
**Zero**onto**Rows**.- Right-click on
**SUM(Zero)**and Select**Dual Axis**.

- Right-click on
- In the
**Marks Panel**, go to**Y**and remove the**Measure Names**from**Color**. - In the M
**arks Panel,**go to**SUM(Zero)**.- Remove
**Measure Names**from**Color**. - Change the
**Mark Type**to**Text**. - Drag
**Category**from**Color**to**Text**.

- Remove

You should not see the following:

We have gone a long way and the only think left to do is to adjust the cosmetics of the Venn Diagram:

- Hide the Headers.
- Remove Grid and Zero lines.
- Adjust the Labels.
- Adjust the Tooltips.

and with these finishing touches, you should finally have the following:

and boom, we are done with probably the most complicated article I will most likely write, but now we have a Venn Diagram that can be selectable. Granted, the mathematics involved is very tricky but I hope you can see that the options for drawing in Tableau are endless.

You can see and interact with my visualisation on Tableau Public at https://public.tableau.com/profile/toan.hoang#!/vizhome/VennDiagrams_0/VennDiagrams

## Summary

I hope you all enjoyed this article as much as I enjoyed writing it, if so, please do share this article with fellow Tableau addicts and spread the love. Do let me know if you experienced any issues recreating this Visualisation, and as always, please leave a comment below or reach out to me on Twitter @Tableau_Magic.

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