It’s Community Month at #WOW2024 HQ, and for the first challenge, Jack Hineman (a long time participant of WOW) asked us to create gauge charts using map layers. Not only that, he wanted them displayed in a trellis format, with a specific requirement to ensure the number of columns was always >= number of rows displayed. Errr…..

This was tough! I tried to start the challenge one evening and after pouring through Ken Flerlages’s blog post that was referenced, reading the hints, and looking at Jessica Moon’s Tableau Public page referenced, I was none the wiser. The blog post did not mention map layers at all in building a gauge, and was purely mentioned as inspiration for the design of the gauge.

I happen to have some time off work, so reattempted the challenge the next day. After several hours, I got there, somehow! I did another google : “Gauge charts in Tableau” and hit upon this blog, which gave me a few pointers, although most of the time it really was a lot of trial and error based on Jack’s hints, and to be honest I surprised myself that I actually hit all the requirements, except one, without the need to look at the solution.

The one thing I had to look at was the calculations required to get the trellis to always have more columns than rows. My ‘go to’ formula didn’t work. More on that later.

As for my solution… well it’s a solution…. how elegant/efficient it is – who knows. It was something built very much in stages as I tried to get my head around what was being asked. As I rebuild as part of the process I go through when writing this blog, I may find ways of improving what I did to start with. I will do my best to explain what I think is going on, what my thought process was, but apologise in advance if you get to the end of all this, and still don’t have a ‘scooby’ 😦

Strap yourself in! This is going to be a long one!!!!

Modelling the data

Connect to the provided data source and create relationship calculations to relate Manufacturers to Gauge_Definition with 1=1 and Gauge_Definition to Gauge_Points with 1=1 as well.

Understanding the data

Let’s start by looking at the data provided. Jack provided 3 data sets:

Manufacturers

A simplified instance of Superstore just listing Manufacturers with Sales & Profit data.

Gauge Definition

A data set of 1 row essentially containing some ‘constants’ to be referenced within the challenge

• Gauge Success Amount = 0.15
  • Profit Ratios >= to 0.15 (15%) are deemed successful. This is essentially the Goal indicator value.
• Gauge Concern Amount = 0
  • Profit Ratios >=0 (but < 0.15) are deemed a concern
• Gauge Start Profit Ratio = -0.3
  • The left hand point on the semi-circular gauge should indicate a -30% profit ratio
• Gauge End Profit Ration = 0.3
  • The right hand point on the semi-circular gauge should indicate a 30% profit ratio
• Gauge Success Pct of Gauge = 0.75
  • 15% Profit Ratio represents 75% of the gauge displayed (ie 0% of gauge = -30% Profit Ratio and 100% of gauge = 30% profit ratio)
• Gauge Concern Pct of Gauge = 0.5
  • 0% Profit Ratio represents 50% of the gauge displayed.

Gauge Points

This is essentially a template/scaffold to help build the gauge and the various features on the gauge. It defines all the points that need to be plotted and in most cases then connected to create the various ‘shapes’ displayed eg the gauge semi circle for the actual profit ratio and the legend indicator; the small angled rectangle that represents the goal ‘reference line’; the positions for the 3 labels.

To start getting an understanding, let’s just focus on Point Type = Actual and Point Segment ID = Background

This is the data to build the complete grey semi circle of the main gauge. 50 rows represent points on the inner arc of the semi circle (Point Arc = In). They all have a Point Radius = 0.43 (ie the distance from the 0,0 centre position of a circle to the bottom edge of the gauge is 0.43). The other 50 rows represent points on the outer arc of the semi circle (Point Arc = Out). They all have a Point Radius = 0.58 (ie the distance from the 0,0 centre position of a circle to the top edge of the gauge is 0.58). Point Angle Rads defines the angle in radians (rather than degrees) from the circle centre to edge of the circle. The Point ID defines the order to ‘join the dots’ when the points are made into a polygon.

Here’s a diagram to help try and explain the maths we’re going to need to use based on the data we have

For each point on the circle, we will need to identify the x & y position of where the radius intersects the edge of the circle. We know the angle, and we know the radius, so we can use trigonometry to work that out, and then use the MAKEPOINT() function in Tableau to covert that into a spatial/geometric field to use on a map.

Let’s do this in Tableau.

Create field

X

[Point Radius] *SIN([Point Angle Rads])

Y

[Point Radius] * COS([Point Angle Rads])

Note – based on my diagram above, X = a and would be derived from the Cosine of the angle, while Y = o and be based on the Sine of the angle. However, Jack gave hints based on the above calcs which hold true if you adjust the diagram and assume the angle is positioned between the y-axis and the radius, rather than the x-axis and the radius.

Now create the point

Geo

MAKEPOINT([X],[Y])

On a sheet, add Point Type to Filter and set to Actual, and add Point Segment ID to Filter and set to Background.

Double click on Geo to automatically add Longitude and Latitude fields to the sheet.

We have the basics of a semi-circle… not in the right direction, but it’s something… Add Point ID to Detail, then click the Swap Axis button and hey presto…

It appears a bit more ‘ovel’ than circular as the axis aren’t aligned, so don’t worry about this – set the display to Entire View will help. Then change the mark type to Line, move Point ID to Path and then change mark type to Polygon.

We now have a filled semi circle. We’re not going to use this sheet, but hopefully, this has helped a bit with some fundamental understanding.

When building we’re going to be using map layers (and at this point, we can’t add a layer to this sheet). We’ll also be defining calculations based on which feature of the viz we’re focussed on, as we can’t apply filters to the sheet (if you remove the ones applied, it will look a little crazy!). But if you change the Point Segment ID filter to Goal, you’ll get the shape of the goal indicator ‘reference line’.

You might want to play around with the filters to examine the behaviour.

Are you still with me…? Take a break, grab a cuppa, we haven’t even started building yet, but I’ll still be here when you get back 🙂

Setting up the map layers

Using Jack’s hints, create a field to help ‘initialise’ the map layers

Zero

MAKEPOINT(0,0)

Double click this to create a basic ‘map’ with a single point.

Then drag another instance of Zero onto the canvas and drop on the Add a Marks Layer section that appears

You’ll now have 2 marks layers, which means whatever we now do, we can always add more.

Building the Gauge Background & Legend layer

Note – in building I ended up with more mark layers than Jack suggested. I’ve subsequently seen other versions but am sticking to what I managed for now.

The first layer I’m going to build is the ‘grey’ semi circle of the main gauge and the coloured legend ‘inner’ semi circle.

I want to identify those points only.

Geo: BG-Legend Layer

IF [Point Type] <> ‘Label’ AND [Point Segment ID] IN (‘Background’, ‘Concern’, ‘Failure’, ‘Success’) THEN [Geo] END

On the Zero marks card, drop this field directly on top of the COLLECT(Zero) to replace it. Add Point ID to Detail, then flip the axis using the switch axis button. Add Point Segment ID to Colour and adjust the colours of the Background, Failure, Concern and Success values to suit.

Change the mark type to polygon, and move Point ID to Path. Name this layer BG & Legend

Building the Actual Layer

Create a new field

Profit Ratio

{FIXED [Manufacturer]: SUM([Profit])/SUM([Sales])}

and format to % with 1 dp.

We need to understand where on the gauge, the Profit Ratio for each Manufacturer falls. We know that the gauge starts at -30% Profit Ratio (ie 0% of the gauge is equivalent to -30% Profit Ratio) and the gauge ends at +30% Profit Ratio (ie 100% of the gauge is equivalent to +30% Profit Ratio). Therefore if the Manufacturer’s Profit Ratio >= 30% it fills 100% of the gauge, anything less needs to be partially through. We can calculate this (using one of Jack’s hints) with

PR % of Gauge

([Profit Ratio] + [Gauge End Profit Ratio]) / ([Gauge End Profit Ratio]- [Gauge Start Profit Ratio])

To then determine the angle in degrees (and again using Jack’s hints), we want to find the proportion of 180 degrees that the PR % of Gauge represents, and then take off 90 degrees based on the gauge rotation.

PR Angle (Degrees)

([PR % of Gauge] * 180)-90

We can then convert this to radians

PR Angle Rads

RADIANS([PR Angle (Degrees)])

This gives us information to help determine a singular point on the gauge we need to ‘draw’ up to. But I want to ‘draw’ a polygon that goes from the left end (-30% mark) to this point, and for this, I need to know all the other points up to that point.

The way I came up with isn’t what Jack did. My result means I don’t get an exactly accurate marker, but it is so close to it’s position, and is ‘good enough’ for the viz type and how it’s being displayed.

To understand what I did, build out a tabular sheet that is filtered to Manufacturer = Hon and Point Type = Actual, and shows Manufacturer, Point Segment ID and Point ID on Rows with Point Angle Rads, Profit Ratio and PR Angle Rads as measures.

The Profit Ratio for the Manufacturer =Hon is 6.4% which is at an angle of 0.34 radians around the semi circle.

You can also see that while we have values for the Point Angle Radians field associated to the Point Segment ID = Background, we don’t have any for the Point Segment ID = Actual, as this is what we’re trying to find out.

Given that I know that all the Point Angle Radians values associated to the Point Segment ID = Background build a complete semi circle, I figured, to display up to my ‘actual’ Profit Ratio, I just want to get all the points associated to background which are less than the PR Angle Rads value.

PR Point Angle Radians

IF [Point Angle Rads] <= [PR Angle Rads] THEN [Point Angle Rads] END

Pop this into the table, and when you scroll down, you’ll see I’ve only got values in my new field up to where the PR Angle Rads is less

Using this field, I’ll create some new X & Y fields which I can make make into a spatial field

X (actual)

[Point Radius] *SIN([PR Point Angle Radians])

Y (actual)

[Point Radius] * COS([PR Point Angle Radians])

Geo – Actual

IF [Point Type] = ‘Actual’ AND [Point Segment ID] = ‘Background’ THEN
MAKEPOINT([X (actual)], [Y (actual)])
END

On the Zero(2) marks card, Replace the COLLECT(Zero) pill with the Geo – Actual pill by dragging the latter and dropping it directly on the former. Add Point ID to Detail.

It’s drawing the points for a complete semi-circle, as every Manufacturer is being included. To help get the rest of the display right, for the various permutations, add Manufacturer to filter and filter to Hon, Bush, Logitech and Xerox. Add Manufacturer to Columns too. You should now see the marks stop at various positions around the arc. The filters will be adjusted later when we tackle the trellis.

Change the mark type to polygon and move Point ID to Path. Rename the layer to Actual.

For the colouring, we need to determine the RAG status of each Profit Ratio – where does the PR % of Gauge sit in comparison the constants we know

Actual RAG

IF [PR % of Gauge] <= [Gauge Concern Pct of Gauge] THEN ‘Failure’
ELSEIF [PR % of Gauge] <= [Gauge Success Pct of Gauge] THEN ‘Concern’
ELSE ‘Success’ END

Add this to the Colour shelf and adjust accordingly.

Building the Goal Indicator Layer

Create a new spatial field

Geo: Goal Layer

IF [Point Type] = ‘Actual’ AND [Point Segment ID] = ‘Goal’ THEN [Geo] END

and then drag this onto the canvas and drop on the Add A Marks Layer option.

Change the mark Type to Polygon and add Point ID to path. Add Point Segment ID to Colour and adjust the colour of the Goal value to suit. Rename the layer to Goal.

Building the Label layer

Create a new spatial field

Geo: Labels

IF [Point Type] = ‘Label’ THEN [Geo] END

and then drag this onto the canvas and drop on the Add A Marks Layer option. Add Point Segment ID to Detail. 3 marks should now displayed in the positions we need them

This bit took a bit of time to get right, as I had 3 requirements I wanted to satisfy: 1 – display a text or a numeric field as a label depending on what label I wanted to display (I attempted to have a single ‘label’ field converting numbers to strings with the relevant formatting, but the Profit Ratio % just wouldn’t show how I wanted when converted to string); 2 – adjust the colour of (some) of the labels depending on the RAG status of the profit ratio value; 3 – adjust the size of the Profit Ratio label based on how many gauges were displayed.

I needed several label fields

Label: Goal

IF [Point Segment ID] = ‘Goal’ THEN [Gauge Success Amt] END

formatted to % with 0 dp.

Label: Manufacturer-Fail

IF [Point Segment ID] = ‘Manufacturer’ AND [PR % of Gauge]<=[Gauge Concern Pct of Gauge] THEN [Manufacturer] END

Label: Manufacturer-Concern

IF [Point Segment ID] = ‘Manufacturer’ AND ([PR % of Gauge]<=[Gauge Success Pct of Gauge] AND [PR % of Gauge]>[Gauge Concern Pct of Gauge]) THEN [Manufacturer] END

Label: Manufacturer-Success

IF [Point Segment ID] = ‘Manufacturer’ AND [PR % of Gauge]>[Gauge Success Pct of Gauge] THEN [Manufacturer] END

Label: PR-Fail

IF [Point Segment ID] = ‘BAN’ AND [PR % of Gauge]<=[Gauge Concern Pct of Gauge] THEN [Profit Ratio] END

formatted to % with 1 dp

Label: PR-Concern

IF [Point Segment ID] = ‘BAN’ AND [PR % of Gauge]>[Gauge Concern Pct of Gauge] AND [PR % of Gauge]<= [Gauge Success Pct of Gauge] THEN [Profit Ratio] END

formatted to % with 1 dp

Label: PR-Success

IF [Point Segment ID] = ‘BAN’ AND [PR % of Gauge]>[Gauge Success Pct of Gauge] THEN [Profit Ratio] END

formatted to % with 1 dp

Add all these fields to the Label shelf, and adjust the label so that all are positioned on the same line, with no spaces, and add a carriage return beneath the text. Colour each field accordingly (DO NOT ADJUST THE FONT SIZE).

Change the mark type to text and align the label top centre. Rename the mark type to Labels and Disable Selection

To adjust the size of the labels, create a new parameter which we’ll need for the trellis.

pShowTop

integer parameter, defaulted to 7 which is a range from 5 to 81 with a step size of 1.

Show the parameter.

Create a new field

Label: Size

IF [Point Segment ID] = ‘BAN’ THEN [pShowTop]
ELSEIF [Point Segment ID] = ‘Manufacturer’ THEN 60
ELSE 80 END

We want the size of the BAN label to decrease as the number of manufacturers displayed increases.

Add this filed to the Size shelf as a continuous dimension (green pill, not aggregated).

Edit the Size legend so that sizes vary by range, the range is reversed, and the range starts from 1 to 81. Adjust the mark size range slider to a suitable start and spread.

As you change the value of the pShowTop parameter, the Profit Ratio BAN should adjust in size.

Format Sales and Profit to be $ with 0dp and to display as () when negative, then on all marks cards, add Manufacturer to Detail and Sales, Profit, Profit Ratio and Actual RAG to Tooltip, and adjust Tooltip on all the layers to suit.

Finally remove all gridlines/zero lines/axis ticks and hide the longitude & latitude axis. Hide the null indicator.

Building the Trellis

So now we’ve got the core viz nailed, we need to address the layout, which is to show a gauge for each of the top n manufacturers based on Sales. This means we need to have the gauges indexed/ranked from 1 to n based on total Sales, and then arrange in a grid so that top left is the manufacturer with the highest sales, and bottom right is the manufacturer with the lowest sales. For this we need to assign a row and column number against each manufacturer.

There are multiple blog posts about creating trellis charts. My go to post has always been this one by Chris Love, especially when the requirement is for the trellis to be dynamic (the number of rows/columns can vary) depending on the number of items to be displayed.

However in this instance, using the calculations referenced in the blog doesn’t meet the requirement of ensuring there are more columns than rows. This was an area that got me stumped. As a result, I finished the viz with a version that utilises my ‘go to’ calculations (published here), before then looking at Jack’s solution to get the calculations, which are

Cols Count

//If Rounded value = Value without Round then no remainder, use that number
if SIZE()/round(SQRT(SIZE()),0) = int(SIZE()/round(SQRT(SIZE()),0)) THEN SIZE()/round(SQRT(SIZE()),0)
//Otherwise add 1 to the number of columns
ELSE int(SIZE()/round(SQRT(SIZE()),0)) + 1
END

Size() is reflective of the number of items (in this case Manufacturers) to be displayed… as I write this down, for this specific instance, you could probably replace SIZE() with the parameter pShowTop.

Rowsv2

//For Each Manufacturer, what Row should it be in the Trellis?
//Rank the Manufacturer, Find the Integer portion when dividing by # of Columns
int((INDEX()-1)/ [Cols Count])

Colsv2

//For Each Manufacturer, what Column should it be in the Trellis?
//Rank the Manufacturer, Find the Remainder when dividing by # of Columns
int((INDEX()-1) % [Cols Count])

Make both Rowsv2 and Colsv2 discrete.

Add Rowsv2 to Rows and Colsv2 to Columns. Remove Manufacturer from Columns. It’ll look a bit odd, but be patient.

Edit the Manufacturer pill on the Filter shelf. On the General tab, select None, to remove everything from the filter, then on the Top tab adjust to be based on the top pShowTop by Sales

Now edit the table calculation associated to the Rowsv2 pill, so that it computes by specific dimensions and every field except Point ID is selected. Ensure Manufacturer and Point Segment ID are listed at the top in that order. Set the level to be Manufacturer and apply a custom sort based on Sum of Sales descending

As this is a nested table calculation, select the drop down arrow at the top and apply the same settings to the nested Cols Count field.

Then do exactly the same again for the Colsv2 table calculation settings. If all has been applied successfully, then you should get a grid

where you can then adjust the pShowTop parameter

Hide the Rowsv2 and ColsV2 fields from displaying (uncheck show header). Show the Longitude axis, and fix it to start at 0 but end ‘automatic’. Then hide the axis again (this ensures the arc lands on the row divider).

Then add the viz to a dashboard. My published version based on the trellis using Jack’s calculations is published here.

If you’ve made it to the end – well done! It was a bit of a marathon to do the challenge and another to write this blog. I’m sure it’s been quite an effort to read too, but hopefully you’ve learnt something, and I’ll certainly be referencing this again when a map layer and/or gauge based scenario occurs again.

Happy vizzin’!

Donna