Symbol Map

$image\symbmap.gif$ Symbol maps display a scaled symbol proportional to the boundary object's associated data value. Bivariate data can be displayed by varying symbol color from a separate data column. The symbols may be repositioned relative to the boundary object by using the Move Centroids command.

Symbol maps can be made for polygons, polylines, or points.

For polygons, the scaled symbols are drawn at the area's centroid (geographic center). The areas use the default fill and line properties, or you can set unique fill and line properties for each area on the map.
For polylines, the scaled symbols are drawn at the midpoint along the curve.
For points, the scaled symbols are drawn directly on top of the point symbol. If the scaled symbols are open, like an open circle with no fill, you can see the point symbol beneath the symbol map symbol. To avoid this, disable the display of the point symbol by selecting the symbols and changing the color to white. The symbol map symbols are still drawn, but the point location symbols are not visible. Alternatively, you can use the View | Show Objects command and turn off the display of the point symbols by unchecking the Symbol box and then checking the Theme of hidden object box. The symbol map symbols are still drawn, but the point location symbols are not displayed.

Creating and Editing a Symbol Map

Create a symbol map by selecting a layer with linked boundary objects. Then, click the Map | Create Map | Symbol command .

See Creating and Editing Thematic Maps for information on creating a maps, changing a map to another map type, and changing map properties.

Symbol Map Properties

You can set the symbol type as well as other options in the Property Manager. The Property Manager for a symbol map contains General, Symbol, Data Labels, Info, and Map pages. Click the preceding hyperlinks for information on properties in each of the property manager pages.

Map Page

Properties that are unique to symbol maps are edited on the Map page of the Property Manager.

Edit symbol map properties in the Map page of the Property Manager.

General

The Proportional properties list selects which properties are proportional to the data in the Variable column on the General page. You can select Size, Color, or Size and color in the Proportional properties list.

Position

The centroid is the geographic center of an polygon, the midpoint along a polyline, or the location of a point. The centroid location can be moved for all polygons, polylines, or points. The Centroid offset is used to offset each symbol from its corresponding position. Center, Left, Right, Above, and Below position the symbol in the specified direction. User defined enables the X and Y boxes so you can enter any arbitrary offset amount. The offsets must be specified in page units.

Click the Origin button to specify the origin of the symbol. The symbol is positioned, rotated, and scaled about the origin. Clicking the Origin button displays the Symbol Origin dialog with some cross hairs in a box. The intersection of the cross hairs represents the symbol origin, and the box represents the limits of the symbol. Use the horizontal and vertical scroll bars to position the origin

Size

Symbol size Proportional method is used to determine the relative size of the symbols. Linear makes the height and width of each symbol directly proportional to its data value, while Square root makes them proportional to the square roots of their values. Linear should be used if your symbol is very narrow (like a bar), since it results in each symbol's height being proportional to its data value. Otherwise, Square root should be used, since it results in the symbol's area being proportional to its data value. Studies show the viewer mentally compares the areas of two symbols and not their heights.

The box containing symbol size and data values allows you to specify how much the symbols are scaled. Enter a minimum value into the Minimum size field, and a maximum value into the Maximum size field. The smallest data value is drawn with the minimum width and height. The largest data value is drawn with the maximum width and height. All data values in between are scaled proportionally. You can use the arrows to increase or decrease each value, or type the size you want. The size is specified in page units.

Click the Map min size to data value of 0 check box to associate the minimum symbol size with a data value of zero. The Use absolute data value option must be activated on the General page of the Property Manager for the Map min size to data value of 0 property to be available.

Color

Select the data column for proportional color in the Data column list.

Select fill and line colors by clicking on the color bar next to either Fill colors or Line colors. Click the to open the Colormap dialog and create a custom colormap for the line or fill.

Negative Data

When Size is the selected Proportional properties item, the Negative Data group is available. The Negative Data options specify a color for negative data values if desired. Click the Specify color for negative values check box to make symbols with negative values a separate color. Click the Fill color or Line color lists to select a color in the Color Palette. Click the buttons to open the Colors dialog and select a custom color.

Angle

Symbols can be rotated in a symbol map uniformly or by using information in a column in the data file. The symbol rotation can be entered as angles (degrees) or the angle information can be calculated based on the column's data in relation to the minimum and maximum angle values.

Select either Uniform or From data in the Angle method list. The Uniform angle method applies one angle to all the symbols in the map. Use the slider bar to change the symbol angle.

When From data is selected, symbol angles are specified by an angle column or proportional to data values in the specified data column. Select the data column for specified angles or proportional angles in the Angle column list. The Angle column should contain numeric values in degrees if Proportional across data is not checked.

Click the Proportional across data check box if the Angle column contains map data and not specific symbol angles in degrees. Use the slider bar to set the Minimum angle rotation for the smallest data value symbol. Use the slider bar to set the Maximum angle rotation for the largest data value symbol. The remaining symbols are rotated in proportion to the minimum and maximum values and their symbol angles.