Sean Miller was back this week to set this challenge to recreate a ‘rat sighting’ map using hexbins. I’ve only used hexbins in other #WOW challenges, so needed a bit of a refresher (the previous challenges pre-dated my own blog, so I couldn’t use myself as a reference). A quick google for ‘tableau hexbins’ and I found a variety of articles that provided the refresher needed.

Sean also used the opportunity to apply some other crucial skills – adding custom shapes and custom colour palettes, which I recommend is the first step you do in completing this challenge.

Adding custom shapes

Download the hexagon shape provided by Sean, and then save it into a folder in your …My Tableau Repository\Shapes directory. I have a folder called ‘Custom’ where I place random shapes I need. This post will help you out if you’re having difficulty with any of this.

Adding custom colour palette

Open a text editor such as Notepad, then open the preferences.tps file that is located in your .. My Tableau Repository directory. Copy & paste the block of code provided by Sean between the opening and closing <preferences> tag. Save the file and close the text editor. This post will help if you’re having trouble.

Building the map

The provided rat sighting data set contains a Longitude and Latitude value for every rat sighting since 2010.

Hexbins provide a way to group (bin) these Lat & Long values together. The size of the bin is typically determined by a parameter, so lets first set this up

pRatio

integer or float parameter which I set to a default value of 250 (Sean didn’t specify the value he’d used, but trial and error suggested to me this looked ‘about right’).

Now we can build the bins

HexbinX

(HEXBINX([Longitude]*[pRatio], [Latitude]*[pRatio])) / [pRatio]

Edit the geographic role of this field to be mapped to Longitude (right click on field -> Geographic Role).

HexbinY

(HEXBINY([Longitude]*[pRatio], [Latitude]*[pRatio])) / [pRatio]

Edit the geographic role of this field to be mapped to Latitude.

Add HexbinX to Columns and HexbinY to Rows. Modify each field so that it is a continuous dimension.

Change the mark type to Shape and select the hexagon shape you saved earlier.

Add the auto generated ‘count of dataset’ (Count of Rows) field to Colour, and adjust the colour to use the OrRd-5 palette you added earlier. Ensure to set the palette to Reversed.

Set the Tooltip so it doesn’t display anything on hover, and add Borough to the Detail shelf (this is needed for the interactivity later). Hide the nulls indicator that displays in the bottom left (right click -> hide).

On the Map menu, select Map Layers, and set the background style to dark.

Using the map controls, zoom in and pan to the left slightly, so the coloured area is mainly central and there’s less ‘sea’ at the bottom. It’s likely that you may need to adjust further once you’ve placed the map on the dashboard. But before publishing, we want to turn the map controls off, to prevent a user from shifting the display (Map -> Map Options -> uncheck all options).

Building the Bar Chart

On a new sheet, add Borough to Rows and Count of Rows to Columns. Add Borough to Filter and exclude Null and Unspecified. Sort the rows descending. Adjust the colour to suit.

Show mark labels, but only display the max & min values. Format the Count of Rows pill so the labels are displayed in K to 2 dp.

Hide the axes, right align the row label headings, adjust the tooltip. Hide the column heading. Remove zero lines and axis rulers. Set the background colour of the worksheet to ‘None’ (ie transparent).

Further formatting is required, but this is best done after the sheet is added to the dashboard, as you’ll lose visibility of the text at this point.

Creating the dashboard

Add the map to a dashboard, and remove all the additional containers/legends etc that are added, and the sheet title. Then add the bar as a floating object and position bottom left. Fit to entire view. Edit the title so it contains the ‘on hover’ instruction and format in light grey font.

Now you can format the row labels, the row headings and the gridlines to be appropriate colours – light grey rather than white.

Add a dashboard highlight action that on hover of the bar chart, highlights data in the Map

Then add floating text boxes and add the title and description. I ended up adding a text box just containing the OH, and then another position just below containing RATS! and then the description, as otherwise the carriage return between OH & RATS! made the spacing too wide. I used the controls on the layout tab to ensure both text boxes were positioned at the same x-coordinate.

Hopefully, you should now have a beautiful looking viz. My published version is here.

Side note – When I first started building this I tried from memory, and didn’t quite get things right. I then adjusted various fields as described above, but when I then tried to add the Count of Rows to Colour, I was only ever getting a value of 1 against each bin. I double & triple checked all the calcs and couldn’t see any issues. It was very weird. I simply ended up closing down my workbook and starting again from scratch and all was fine. I’m just letting you know this in case you too come across any oddities during your build, and things don’t behave as expected. It meant, what was ultimately quite a straight forward build (once I got the calcs right), ended up involving more time and head-scratching than really required 😦

Happy vizzin’!

Donna