Changing Data Classes


A data class is a grouping of data on a thematic map. For example, persons in Arizona can be divided into age groups:


-- Group 1: 0-17 years

-- Group 2: 18-28 years

-- Group 3: 29+ years


Each of the age groups 0-17, 18-28, and 29+ represent a data class. By default, a thematic map uses the natural break classing method, yellow to green color ranges, and the number of classes appropriate for the data you choose. To change any of these defaults, see below:


Number of Classes

Class Color

Level of Transparency

Classing Method




Number of Classes

  1. In the map side menu, click the colors and data classes button .

  2. Click the drop-down menu next to number of classes to change the number of classes used to display the data (if you choose 6, 6 colors will be used to display the data). Thematic maps have a minimum of 2 classes and a maximum of 7 classes.


The map displays with the newly created classes.



Class Colors

  1. In the map side menu, click the data classes and colors button .

  2.  Click one of the color picker buttons to choose the beginning or ending map theme color.

The color window will display.

  1. Slide the color bar up and down to change colors.

  2. Use the shade selector to click in the left side window and select a shade.

  3. Preview the color in the preview window and click OK to select the color.



The color window disappears and the selected color displays next to the color picker button.



The map displays with the newly created class colors.



Level of Transparency

The level of transparency determines how easy it is to view underlying map features. A level of 100 makes the color completely transparent and a level of 0 makes the color completely opaque, meaning you cannot see any underlying map features.

  1. In the map side menu, click the data classes and colors button .

  2. Select a value from the transparency drop-down menu.


The map will display with the newly selected transparency level.



Classing Method

  1. In the map side menu, click the data classes and colors button .

  1. In the classing method drop-down box, click a classing method:

-- Natural Breaks - identifies groupings that naturally exist in the data

-- Quantile - units of measurement are ranked and then divided equally into the number of classes

-- Equal Interval - divides data into classes of equal size

-- User Defined -- Enter values to define the breaks for each class. The first and last values are entered to reflect the minimum and maximum data values. Enter values in the right hand column to create data classes. The lower values in the left hand column are automatically calculated.

  1. Click GO


The map displays with the newly created data classes.



Error Messages

You may encounter some of the following errors relating to changing data classes.


Please enter valid data class values

Check for:

-- Missing input from one of the fields

-- Invalid data value; letters instead of numbers, too many numbers



See Also

Creating a Thematic Map

Reference Maps

Finding a Location and Repositioning a Map

Changing Map Boundaries

Placing Map Markers

Basic Map Tools