Changing Data Classes

 

A data class is a grouping of data on a thematic map. For example, the number of people 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

 

 

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Number of Classes

1.    In the map side menu, click the colors and data classes button.images\ebx_68067390.gif

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.

3.    Click GO.

 

The map displays with the newly created classes.

 

 

Class Color

 

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

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2.    Click the color picker button, images\img08966.gif to choose the map marker color

 

The color window will display.

 

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

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

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

 

images\ebx_334874372.gif

 

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

 

6.    Click GO

 

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

images\ebx_68067390.gif

2.    Click and move the arrow on the transparency slider bar from 0 to 100 to change how transparent the colors appear on the map

3.    Click GO

 

The map will display with the newly created transparency levels.

 

Classing Method

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

images\ebx_68067390.gif

2.    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.

3.    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

Showing Statistical Significance

Creating a Thematic Map

Reference Maps

Finding a Location and Repositioning a Map

Changing Map Boundaries and Features

Placing Map Markers

Basic Map Tools

Maps Overview