Dot density themes are sometimes called dot distribution maps because they show where particular data characteristics occur. It uses dots or other symbols to represent the number of occurrences of a given data characteristic in a particular location. Each dot or symbol used on the map may represent a single entity (one dot = one person) or as a one-to-many entity (one dot = 1000 people). The data is read from each MAP Layer and MAP Themes quickly styles the data using Adobe Illustrator symbols and graphic styles.
Since dot density maps are most useful for showing where particular data occur, they only work on area MAP Layers. Most often, symbols are used to represent data occurring within a bounding polygon such as a census tract, zip code or county. Use caution when analyzing dot density maps, it should be understood that the dots or symbols do not always indicate the exact location of the data.
Using Dot Density Themes
Create New Dot Density Theme
To create a new Dot Density theme, click the Add Map Theme button in the MAP Themes panel. Alternatively, choose New MAP Theme from the MAP Themes panel options menu. This opens the New MAP Theme dialog box, where the theme name, theme type, and feature type for a new Dot Density theme are specified.
Dot Density themes are displayed in the MAP Themes panel. To edit a Dot Density theme, double-click it or select Edit "Theme Name" from the MAP Themes panel option menu. This opens the Edit Dot Density Theme dialog box.
The Edit Dot Density Theme dialog box is where attribute, density and symbols are chosen.
Dot density is created on a per layer, per attribute basis. When an attribute is chosen from the drop-down list, click the Load button. The data range displays the minimum and maximum values for that attribute. These values should be taken into account when determining a one-to-many dot density and dot value.
A dot value of 1.00 represents a single (one-to-one) entity. A dot value greater than 1.00 represents a group (one-to-many) entity. See Considerations for Dot Density Maps.
Choosing dot size is a subjective decision based on visual perception limits and aesthetics (see Considerations for Dot Density Maps). There are two main options to style dots: simple and symbol. Choose the Specify option to use simple dot styles from the drop-down list. By default, the Appearance options are in Custom Mode. Click the toggle button to switch to Graphic Style mode, where a graphic style can be chosen from the drop-down list. Alternatively, choose the Use symbol option to use symbols sourced from the Adobe Illustrator Symbols panel. Adjust the scale and opacity as necessary. Check the Always regenerate dot positions when applying to randomize the dot positions when the Apply button or Apply MAP Theme button in the MAP Themes panel is clicked.
Only basic appearances can be applied to dot density dots. Adobe Live Effects, graphic styles with opacity, multiple strokes and other non-basic appearances or effects cannot be used.
After a Dot Density MAP Theme is applied, the effect is listed in the Adobe Illustrator Appearance panel. Select an area containing the dot density effect and click Dot Density in the Appearance panel to open the Dot Density dialog box. This dialog box differs from the Edit Dot Density Theme dialog box. The Dot Density dialog box can be used to fine tune the dot density appearance of individually selected areas instead of making a global change.
Considerations for Dot Density Maps
When creating one-to-many dot density maps, several considerations should be noted: enumeration units, dot size, dot value and dot placement. The scale, size, shape, and distribution of data across enumeration units (e.g. census tracts or block groups) can cause variations in how a dot density map is patterned. On average, smaller sized and more regularly shaped enumeration units result in a more realistic density map.
The dot value and dot size should be determined together to get an idea of how many dots will populate the map. Take into consideration the minimum and maximum values of the selected attribute. A rounded dot value should be chosen for easy approximation. There is a trial and error phase when choosing the most appropriate dot value and size. Generally, a medium sized dot should be chosen. Small dots produce a widely dispersed dot pattern and may convey disproportionate map accuracy. Large dots produce overly dense dot patterns and hide any noticeable map patterns. As a general rule when an appropriate dot value and dot size are chosen, two to five dots should be seen in enumeration units with the smallest values. MAPublisher allows for automated, random placement of dots.
When the value for a particular feature is lower than the "Dot value", a dot may not be assigned for that object. This happens because MAPublisher only accepts values that are greater than fifty percent of the dot value to be given a dot. For example, if an object has a value of 4,000 and the dot value is 5,000, it will be assigned a dot because it is greater than fifty percent (or 2,500) of the dot value. Alternatively, an object that has a value of 2,000 will not be assigned a dot because it is less than fifty percent (or 2,500) of the dot value.