How to make a Spoke Chart

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Last week at the Chandoo.org Forums, MarnieB asked:

I have been asked to produce a chart that looks like the spokes in a wheel. Lines for each data point that start from the same point in the middle and go out in different directions. The length of the line indicates the value of the data point. There are only 5 or 6 data points.

Lets see how we can produce such a “Spoke Chart” in Excel.

Disclaimer: Before I go too far I want to say that this post isn’t recommending the use of this type of chart. The post is about introducing techniques which you can use as the basis of many custom chart types. The post just uses this chart as a simple example.

 

EXCEL CHART TYPES

Excel doesn’t have a native Spoke Chart in its catalog of built in Chart Types.

As MarbnieB found out, Radar Chart give some level of simulation, but there not ideal for what MarnieB’s boss wanted.

Luckily for us Excel has a Scatter Chart and this chart type can be used as a veritable drawing board for your own purposes.

The Scatter Chart draws lines between sets of coordinates in the X-Y plane.

Typically Scatter Chart are used for Plotting two variables against each other where neither the X or Y axis has a regular occurrence frequency,

But Scatter Charts can also be used for adding custom chart types as we will see below.

 

MARNIEB’s SPOKE CHART

Lets look at MarnieB’s specifications:

  • It should have 5 or 6 spokes
  • Spokes radiate out from a central hub
  • The length of the spokes should reflect the spokes value

So it will look something like this:

(Not drawn to scale)

We can imagine that the center of the Spoke is at a position X=0, Y=0 or (0, 0) on the Cartesian plane.

We can then break up a circle into a number of segments n. MarnieB’s requirements n = 6.

As a full circle is 360 degrees we can see that each spoke will be separated by 360/6 = 60 Deg

Hence there will be spokes at:

  • 0 Deg
  • 60 Deg
  • 120 Deg
  • 180 Deg
  • 240 Deg
  • 300 Deg

The length of each spoke will be supplied by MarnieB.

We can use the Scatter chart to plot each Spoke as a separate series on the scatter chart.

Each series will consist of two points, being the center point (0, 0) and another point at the end of the spoke (x, y).

 

We will need to determine the X and Y values for each end of the spoke.

Using some simple trigonometry we see that:

X = Length * Cos ( angle )

Y = Length * Sin ( angle )

Now we know the angles and lengths and so in Excel we can setup a small table to calculate the X, Y values for each end of the spokes.

Using Excel we need to remember that Excel requires angles in radians. This just requires a simple modification to the formula to:

X = Length * Cos (Radians( angle ) )

Y = Length * Sin (Radians( angle ) )

 

Setup the Chart Series

Before we jump in you can follow along this example using a new Excel file or the worked Example File, Excel 97/03, Excel 07/10.

As mentioned above each spoke will require two points

Point 1, The center of the spoke at 0,0 and a point at X, Y

In Excel we setup a small table of the Inputs including the Point Id, Angle and Length

We can then add some formulas to take the inputs and convert them to X, Y Cartesian coordinates using the formulas described above.

 

Putting the Chart Together

Once you have the Spoke coordinates you can construct the chart

With NO data selected, goto the Insert Ribbon and select Scatter, Scatter with Straight Lines

A blank chart will appear on the Screen

You can resize and shift the chart to a useable location if you require.

Right Click on the Chart and select the Select Data option

The following dialog appears:

Select the Add, button and the Edit Series dialog appears.

The Series Name: is linked to the Spokes Name $A$4

The Series X values: is linked to the two Chart X values: E3:E4

The Series Y values: is linked to the two Chart X values: F3:F4

Ok when complete

You can now go ahead and add the other 5 Series to the chart by selecting the Add button.

Your Select data dialog will now appear like:

And the chart will appear something like:

Cleanup and Format the Chart

We now need to clean up and format the chart

Select and Delete the Charts Title, Chart Legend & Horizontal Grid Lines

Select Each Axis in Turn, Right Click and Format Axis

Set the Minimum and Maximum values to something greater than our data eg: -20, +20 in our example. The Minimum and Maximum for the Horizontal and Vertical axis bust be the same so that the chart scales correctly.

Resize the Chart so that it is approximately square

Leave the axis for now, it is simple to delete them later

Select each spoke in turn

Right Click and select Format Data Series

Set the Marker Options, Marker Fill, Line Style, Line Color to suit your preferences

If you want to add a marker to one end of the line, Select the line, then use the Right/Left arrow keys to select the end you want, Ctrl 1 to Edit the Format of that end only.

Your chart should now be something like:

Add Data Labels

Select each spoke in turn using the Up/Down arrows, then using the Right/Left Arrow keys, select the outer end of the Spoke

Right Click and Add Data Label

A Default value will appear which is the Y Value for the data point

Right Click on the Data Label then select Format Data Label or simply press Ctrl 1

Unclick the Y Value and Tick the Series Name

Repeat for each Spoke.

You may want to change the alignment for some of the Data Labels so they don’t clash with the spokes.

Add Circular Grid Lines

Lets add 3 Grid lines at a Maximum value and at 1/3rd and 2/3rds of that value

First we need to calculate the Grid Values

In cells C22:C24 I added 3 formulas

I have then assigned 3 Named Formulas to the 3 cells

Max_Circle: =$C$22

Mid_Circle: =$C$23

Min_Circle: =$C$24

To make a circle on a Scatter Chart we will need some points for the X and Y values for each point around the circle

To achieve this I will use a few Named Formulas:

t: =RADIANS(ROW(OFFSET(‘1’!$A$1,,,361,1)))

X_1: =SIN(t)*Max_Circle

Y_1: =COS(t)*Max_Circle

X_2: =SIN(t)*Mid_Circle

Y_2: =COS(t)*Mid_Circle

X_3: =SIN(t)*Min_Circle

Y_3: =COS(t)*Min_Circle

 

Lets look at a few of these and see what is going on:

t: =RADIANS(ROW(OFFSET(‘1’!$A$1,,,361,1)))

This formula sets up an Array of 360 values from 1 to 361, corresponding to 1 degree to 361 degrees. This occurs using the formula: = ROW(OFFSET(‘1’!$A$1,,,361,1)) which takes the Row value of an temporary range which is setup from cell A1 and offset 0 Rows, 0 Columns and is 361 rows high and 1 Column wide.

In a blank cell C27 type: = ROW(OFFSET(‘1’!$A$1,,,361,1)) press F9 not Enter

Excel will display ={1;2;3;4;5; … ;355;356;357;358;359;360;361}

1 number for each row, which will be used to represent the degrees of the circle

 

In a blank cell C28 type: =Radians( ROW(OFFSET(‘1’!$A$1,,,361,1))) press F9 not Enter

Excel will display ={0.0174532925199433;0.0349065850398866;0.0523598775598299; … ; 6.2482787221397;6.26573201465964;6.28318530717959;6.30063859969953}

The same array of Degrees now converted to Radians

You can learn more about how this style of formula works by reading the Formula Forensics Series where a number of similar formulas are used.

 

We can now use the Array of Radians to feed the Formula for the X and Y values

Looking at X: the X value of each point will be X = Circle Radius * Cos( t )

Where t is our array of Radians

So for Circle 1, the Maximum Circle the X Values will be

X_1: =Cos(t)*Max_Circle

In a blank cell C29 type: =COS(t)*Max_Circle press F9 not Enter

Excel will display ={14.9977154273459;14.9908624052864;14.9794430213186; … 14.9908624052864;14.9977154273459;15;14.9977154273459}

This is an array of the X Values of the Maximum Circle, all 360 of them.

You can check out the other X and Y values for the other circles yourself.

To add the Circular Grid lines to the chart, Right Click on the Chart, Select Data

This is the same Dialog we saw earlier

Select Add

Series name: =”Max Circle”

Series X values: =’1′!x_1

Series Y values: =’1′!y_1

Note: that we have added the worksheet name and the Named formula to the Series X and Series Y value fields. This serves to reference the Named Formula to this worksheet, sheet “1”.

Select Ok and add the Mid and Min Circles in a similar manner.

Your chart should now be similar to this:

Add Grid Annotation

Add Grid Annotation by adding 3 more series to the chart, 1 series for each annotation point.

We can put a point at the intersection of the 3 circles and the X Axis because we know the radius and the Y value = 0 so the 3 points will be at

(Min_Circle, 0)

(Mid_Circle, 0)

(Max_Circle, 0)

Once again Right Click on the Chart, Select Data

This is the same Dialog we saw earlier

Select Add

Series name: =”Min Annotation”

Series X values: =’1′!Min_Circle

Series Y values: ={0}

We can note that we have used the Named Formula for the Min Circle value as the X Value and that we have used a constant array for the Y value of 0.

Repeat this for the Mid and Max annotation points.

 

Format the Annotation Points

The 3 points you have just added to the chart may or may not be visible

The easiest way to find them is to either

Use the up/down arrow keys to scroll through the Chart series until you see it selected

Or

Select the Chart

Goto the Chart Tools, layout Ribbon and select the Min Annotation series from the drop down list:

If there is a marker showing, set the Marker Style to None

Close the Format Dialog and Right Click on the Marker, Add Data Labels

Select the Data Label and Change it from the Y Value to the X Value

Also change the Label Position to Above

Resize the Chart

Right Click on the outside of the Chart and select Format Chart Area

On the Size Tab, set the Height and Width to the same value

Select the Horizontal Axis and Delete it and repeat for the Vertical Axis

Your chart is now complete

 

DOWNLOAD THE ABOVE FILE

You can download the Example File used above: Excel 97/03, Excel 07/10.

 

OTHER CHARTS DONE IN EXCEL USING SCATTER CHARTS

As you have seen above the Scatter Chart can form the basis of your own custom Charts with the results being limited by your imagination.

Presented below are three Scatter charts where the authors have taken Scatter Charts to the extreme.

 

Hui’s – 3D Pendulums

In 2011, I produced an animated Scatter Chart consisting of 18 x 3D Pendulums in Excel which includes the ability to rotate the chart whilst the pendulums are swinging.

This is a Scatter Chart that consists of about 22 series, 18 for the Pendulums and a few others for the Frames and Axis.

The maths behind the pendulums locations and the rotations is all done via named formulas with a very simple macro driving the animation.

http://chandoo.org/wp/2011/07/06/3d-dancing-pendulums/

Excel Hero – Smith Chart

Daniel Ferry at Excel Hero.com has produced what I consider one of the most amazing charts in Excel I have ever seen.

I don’t make this statement just for the actual modelling of the Smith Chart or the use of Excel and Named Formulas in particular but also for the sheer Beauty that is displayed in the finished chart.

http://www.excelhero.com/blog/2010/08/excel-high-precision-engineering-chart-1.html

ExcelHero - Smith Chart

 

Frankens Team

The Frankens team has published a number of strange charts with a lot of them based on Scatter Charts.

https://sites.google.com/site/e90e50fx/home/creative-and-advanced-chart-design-in-excel

Please note that some of these charts use advanced excel techniques and are not for the feint hearted.

 

Yes the 3 charts above are all Scatter Charts, illustrating the incredible diversity that can be achieved using this tool.

 

WHAT CHART STYLES WOULD YOU LIKE TO SEE ?

What do you think of the techniques discussed above ?

What chart styles would you like to see ?

Let us know your thoughts to the above in the comments below:

 

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15 Responses to “A Gantt Chart Alternative – Gantt Box Chart”

  1. Kenjin says:

    That's a great idea.
    Maybe the planned End Date should be highlight more.
    I don't know how it would look like (nor how to do it yet), but what if instead of finishing the bold line to the best case End Date, it finishes to the realistic End Date?

  2. ross says:

    The idea is ok, I think other project management tools have this, already? Maybe not.

    Gantt charts in my view are about the signal most unless thing in the world, theres no way you can look at one thats more that a little complex and understand what it's telling you. I'm going to write a diatribe on project management at some point, its one of my pet areas I think!! 😉

    The issue I have with this chart Chandoo, is that Tasks need to be linked to each other, so they should inherit the uncertainty, which would mean the as you moved down chart the lines would be miles apart for later tasks, and you might have to add lots of lines for subsequent tasks to cover the various outcome of it's parents.

    Having said that, for the high level board summary, it's a nice way to go, it it appeals to the management 😉

    thanks Chandoo, great post.

    Ross

  3. Cyril Z. says:

    Whoooa !!! That's a very clever idea Chandoo. I really love it.
    I think i'll update my gantt project sheet with that idea soon (remember my template ?)
    @ross : you can link start date to the end date of the previous task in your data. The only problem I still se is to which end date (real ? planned ? best ?) in order to have average amount of information.

    If best end date, you'll tend to increase uncertainty at the end of chain, although if you link to real end date, uncertainty will be decreased too much, leading in both cases to wrong management direction.

    Maybe planned till the task is finished then real will do the job ?

  4. Vijesh says:

    Hey chandoo, this looks good and this would definite add value in production planning / scheduling. Uncertainity in finishing a task is very high in production scheduling and this could give an insight or a bird eye view of possible shipments we can have....

  5. PK says:

    I've always been frustrated by the limitations of gantt charts. Will definitely use this, I've always struggled with how to succinctly communicate the uncertainty of certain tasks without confusing stakeholders.

  6. Andy says:

    I like this, I think it's a very effective way of showing how a timeline can change and which parts of a project need close attention.
    @Cyril / @Ross: I would intially link the the start date to the planned end date of the previous task, with the chart updating when a task has been completed to reflect the true end date.

    Or what about giving a drop-down selection box to allow the user to see the chart based on planned/best-case/worst-case end dates?

  7. Eric says:

    Like the idea. Have found that Excel is more flexible than MS Project for graphical solutions. The "Best Case"\"Worst Case" metrics are theoretically appealing but once the project and\or phase commences their reliability diminishes. A chart like the above that showed Planned Start, Planned End, Replan End Start, Replan End Date, Number of Replans the Start and End Dates, and Actual would provide an active, actionable view of each task\phase. It would also highlight the areas which are riskiest.

  8. Bob says:

    It is always amazing how flexible excel can be.

    My question is how would the chart show a scenario where the date moved up? If a task is dropped or the duration of the task is significantly reduced by applying more people or machinery to the task, the dates will move up.

    The gantt chart has been around for a long time, but it is still quite useful to show progress.

    Cheers,
    B

  9. Shyam says:

    I like the idea but seems bit complicated in case of long projects involving numerous activity.

    Also, reading and explaining is required hence not feasible where plans are just send to audience for approval.

    Cheers
    SY

  10. Peter says:

    Great idea Chandoo,

    When I was reading this idea regarding delivery dates, another thought popped into my mind, how can you show the uncertainty with MONEY!!

    In this case, applies to cost management or even a normal budget, you think?

    Would Box Chart and Gannt Chart help to understand the best case, middle case and worst case when money is spend or planned with these three risks are involved?

    I imagine that this chart could help people who write their budgets get a better understanding of risks affecting their spending.

    Peter

  11. Matthew Galman says:

    Chandoo,

    I like it. How would you display an entry once it has been completed (actual)?

    Thank you,

    Matt

  12. Phil says:

    From what you have shown so far I think that this box Gantt chart is awesome! I think that this could be an extremely useful tool.

    I can't wait to learn how to make my own charts in Excel.

    Will the methods that you are going to teach us work in 2003 as well?

  13. [...] Firday, we proposed a new chart for showing project plans. I chose an ugly name for it and called it Gantt Box [...]

  14. TommyZ says:

    You need to read Eli Goldratt's Critical Chain. The uncertainty you are looking for should be accounted for in a project buffer. Not at each task level.

    Further you should spend time understanding Agile Development. This would have you plan only in 1-3week iterations. This allows you to embrace changes to work not yet started, and for your customer to re-direct your course at regular intervals (after each iteration) throughout your project. keyword search: Agile Scrum

    These items will show you that you are solving a tracking problem for something that you can entirely avoid!

  15. […] Chandoo.org’s  Gantt Box Chart. […]

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