2.3 Data Types, Geographic Roles, Aliases & Default Properties

2.3 Data Types, Geographic Roles, Aliases & Default Properties

Once data is connected and modeled, analysts must configure field metadata within Tableau Desktop. Setting accurate Data Types, assigning Geographic Roles, defining Field Aliases, and establishing Default Properties (such as number formatting and default aggregations) ensures that visualizations render correctly and behave predictably across worksheets.

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Tableau Data Types & Auto-Detection

When Tableau connects to a data source, it automatically inspects the first few hundred rows of each column and assigns a specific Data Type. Data type icons are displayed next to field names in the Data Source page and the Data Pane.

Changing Data Types

If Tableau misinterprets a column (for example, reading a numerical Zip_Code column as a Whole Number # instead of a Geographic String #Abc), you can change it by:

1. Clicking the Data Type Icon directly above the column in the Data Source tab or next to the field in the Data Pane.
2. Selecting the correct data type from the context menu.

EXAM CAUTION: Treating zip codes or phone numbers as measures (numbers) causes Tableau to attempt to sum (SUM(Zip_Code)), producing meaningless numbers. Always convert identification numbers and postal codes to discrete dimensions or geographic roles.

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Dimensions vs. Measures & Discrete vs. Continuous

Tableau categorizes every field along two independent axes:

1. Dimensions vs. Measures:

   • Dimensions contain qualitative, categorical data (e.g., Customer Name, Region, Product Category). Dimensions slice and dice data, creating headers in views.
   • Measures contain quantitative, numerical values that can be aggregated mathematically (e.g., Sales, Profit, Quantity). Measures create axes in views.

2. Discrete (Blue) vs. Continuous (Green):

   • Discrete (Blue) fields create distinct headers and column labels.
   • Continuous (Green) fields create unbroken axes and continuous color gradients.

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Geographic Roles & Spatial Mapping

Assigning a Geographic Role tells Tableau that a dimension's values correspond to real-world spatial locations.

Native Geographic Roles

Tableau natively recognizes standard geographic fields including:

• Country / Region
• State / Province
• County
• City
• Zip Code / Postal Code
• CBSA / MSA (Core Based Statistical Area)
• Airport (3-letter IATA codes)
• NUTS (Nomenclature of Territorial Units for Statistics in Europe)

Generated Latitude and Longitude

When a field with a Geographic Role is added to a view (or double-clicked), Tableau automatically generates two fields in the Data Pane:

• Latitude (Generated)
• Longitude (Generated)

Tableau matches dimension string values (e.g., "Chicago") against its built-in spatial geocoding database to populate lat/long coordinates onto map views.

Custom Geographic Roles

If your data contains custom geographic groupings (such as Sales Territory containing groups of states), you can assign a Custom Geographic Role by right-clicking Sales Territory -> Geographic Role -> Create from... -> select State/Province.

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Field Aliases

An Alias is a custom display label assigned to individual dimension members (the distinct values within a field).

How to Create an Alias

Right-click a dimension in the Data Pane -> select Aliases... -> enter new display names for target values (e.g., changing "US" to "United States" or "N" to "No").

Critical Rules for Aliases

• Does NOT Change Underlying Data: Aliases affect only how values are displayed in tooltips, headers, and legends within Tableau. The underlying database data remains untouched.
• RESTRICTIONS: Aliases CANNOT be created for:
  • Measures (numerical aggregated fields).
  • Continuous fields.
  • Dates.
  • Boolean fields.
• Aliases can be cleared at any time by clicking Reset Aliases in the Aliases dialog window.

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Setting Default Properties

To avoid repeatedly formatting the same field across dozens of worksheets, analysts can set Default Properties in the Data Pane. Right-click any field -> select Default Properties:

1. Default Number Format: Set a measure's default formatting (e.g., Currency with 0 decimal places, Percentage, or Custom Scientific). Every time this field is dragged onto a view, it automatically adopts this formatting.
2. Default Aggregation: Change the default aggregation assigned when a measure is brought into a view. While SUM is the default for most measures, fields like Discount Rate or Temperature should be set to AVG or MEDIAN.
3. Default Color: Assign specific color palettes or encoding rules to a dimension's members (e.g., mapping "Pass" to green and "Fail" to red).
4. Default Sort: Define a custom sort order for dimension members (e.g., sorting Priority as Low, Medium, High, Critical rather than alphabetically).
5. Comment: Enter a textual description that appears in a tooltip when users hover over the field in the Data Pane.