Heat Maps 101 | Calendar Maps

What is a Calendar Heat Map?

A calendar map uses colour encoding to show data over specific dates; this can include showing aggregated data over months, weeks or days. They are useful for understanding and analysing patterns, trends and correlations within the data.

Creating a Single Month Calendar in Tableau

1. Open Tableau Desktop, connect to the data source and ensure that the data includes a date field.

2. Go to a new worksheet, then drag the date field to the ‘Filters’ card and filter to a specific month / year period.

3. Drag the date field from the ‘Data’ pane onto the ‘Rows’ shelf, right-click and select ‘Week Number’ under ‘More’ from the discrete date parts.

Navigation bar showing how to find the week number setting in Tableau

4. Drag the date field from the ‘Data’ pane onto the ‘Columns’ shelf, right-click and select ‘Weekday’ under ‘More’ from the discrete date parts.

Navigation bar showing how to find the weekday setting in Tableau

5. Right-click on the ‘WEEK(Date)’ field on the ‘Rows’ shelf and uncheck the ‘Show Headers’ option. This will hide the week column in the calendar.

Navigation bar showing how to find the sort and format setting in Tableau

6. Right-click on the ‘WEEKDAY(Date)’ field in the ‘Columns’ shelf, select ‘Format’, go to ‘Dates’ and select ‘Abbreviation’ to change the full name of weekday to its three-letter abbreviation.

Navigation bar showing how to find the abbreviation setting in Tableau

7. Right-click on the ‘Date’ header in the calendar and select ‘Hide Field Labels for Columns’. This will hide the ‘Date’ header.

Navigation bar showing how to find the 'hide field labels for columns' setting in Tableau

8. Drag the date field onto the ‘Text’ card, right-click and change the format to ‘Day’ from the discrete date parts. This displays the dates in a calendar month.

9. Drag a measure field that adds meaning to the calendar map, for example, ‘Mean Temperature’, to the ‘Colour’ card. Change the ‘Mark’ type to square. The default colour palette in Tableau is blue-teal. The colour palette can be customised in the ‘Colour’ card. Since this calendar shows the daily mean temperature, an orange-gold colour palette may be more suitable, as we can clearly see that the days in a darker shade of orange have the higher mean temperatures of that month.

Image depicting orange colour gradient in Tableau heat maps

10. Other formatting options:

  • The current calendar format has Sunday as the start of the week. To change the beginning of the week, right-click the data source in the ‘Data’ pane, select ‘Date Properties’ and change ‘Week start’ to Monday.
Navigation bar showing how to find the data properties setting in Tableau
  • Add the correct unit (°C) for mean temperature by right-clicking on the field, select ‘Default Properties’ > ‘Number Format’ > add °C to ‘Suffix’.
Navigation bar showing how to find the custom number setting in Tableau
  • Customising tooltips provides additional information when hovering over or clicking on specific dates.
Image showing Heat Map results
  • Add border to the calendar map by selecting ‘Colour’ card > Border = “White”

11. To make the calendar map interactive, add a Month / Year filter to the calendar. Right-click on ‘MY(Date)’ field in the ‘Filters’ card and select ‘Show Filter’. Click the ‘Ctrl’ key while selecting the ‘MY(Date)’ field in the ‘Filters’ card and drag it to the ‘Rows’ shelf before ‘WEEK(Date)’. The calendar map view changes according to the Month / Year selected.

Image showing final Daily mean temperature Heat Map visualisation in Tableau

Creating a 12-Month Calendar in Tableau

Example of a calendar

1. To create a 12-month calendar, repeat steps 1 – 9 from the previous section. For step two, filter to a specific year, e.g. 2009, instead of a specific Month / Year period. This will provide a single column of days in a week for the entire year.

Image depicting weekday heat map in Tableau

2. Create a calculated field ‘Column Group’ with the following calculation. Drag ‘Column Group’ onto the ‘Columns’ shelf, right-click on the field and uncheck ‘Show Header’ to hide the header.

12 month calendar code excerpt for Tableau

This splits the single column into three columns.

Calendar heat map split into three columns

3. The weeks in each month are not aligned in the same row, to align them, we create a Level of Detail (LOD) calculated field called ‘Week Index’ with the following calculation.

Week index calculation in Tableau

This calculation subtracts the minimum week number at the month-level from the week number at the level of the visualisation to shift the weeks up.

4. Convert ‘Week Index’ from measures to dimensions and replace ‘WEEK(Day)’ field in the ‘Rows’ shelf with ‘Week Index’.

5. To get the calendar map to display 12 months, drag a date field to the ‘Rows’ shelf and select ‘Quarter’ from the discrete date parts. Uncheck ‘Show Header’ for ‘QUARTER(Date)’ field and ‘Week Index’ field.

Week index to week day view in Tableau
Final Mean Daily Temperature 12 month view in Tableau

Summary

Calendar maps are helpful tools for effective time management, scheduling, and visualising patterns across a period of dates. Additionally, they offer a visually intuitive approach to discern time-bound trends, making them invaluable for data-driven decision-making processes.

Not sure what heat map you should be using? Check out our Heat Maps 101 post to get caught up!