Themes

GISDK lets you create and manage themes on a map layer. The theme creation GISDK functions provide extensive control over the parameters of the theme, and let you customize your maps in almost every imaginable way.

You create themes using one of four GISDK functions, all of which have a small number of required arguments, and a long list of options you can use to customize the theme. Other GISDK functions are used to display or hide a theme and to manage the list of themes associated with a map or layer. Here is a quick summary:

GISDK Function	Summary
ClearThemeValues()	Removes the data used to generate a theme from memory
CreateChartTheme()	Creates a pie or bar chart theme on the current layer
CreateContinuousTheme()	Creates a scaled-symbol theme on the current layer
CreateDotTheme()	Creates a dot-density theme on the current layer
CreateTheme()	Creates a color or pattern theme on the current layer
DestroyTheme()	Removes the definition of a theme from the current layer
GetDisplayedThemes()	Gets a list of themes shown on a layer or selection set
GetThemes()	Gets a list of themes defined on the current layer
HideTheme()	Switches off the display of a theme on the current layer
ShowTheme()	Displays a theme on the current layer
TestTheme()	Provides information on the classes created by a call to CreateTheme()

You can create any number of themes for each layer, and use ShowTheme() and HideTheme() to determine which themes are displayed at any given time. For example, you can create ten different color themes on ZIP Codes, and then program menus or a dialog box to let the user choose which theme should be displayed at any given time. This is more flexible than standard Maptitude, which allow you to create only a single color theme on a layer at one time.

When you show a theme with ShowTheme(), you can choose to show it for an entire layer, or only for a selection set. When a theme is applied to a selection set, records in that selection set are shown according to the theme, while records not in the selection set are shown in their default drawing style.

Up to four themes can be displayed on a layer at one time. For point and line features, the four themes can include one color theme, one pattern theme, one chart theme, and one scaled-symbol theme. For area features, the four themes can include one color theme, one pattern theme, one dot-density theme, and either a chart theme or a scaled-symbol theme.

Here is a sample macro that creates a color theme based on State population density, and a dot-density theme based on male and female population. The color theme is shown for all States, while the dot-density theme is shown only for the "High Income" selection set.

Macro "create two themes on the state layer"
SetLayer("States")

// Create the first theme
t1 = CreateTheme("Population Density",	// The name of the theme
"PopDensity",	// The field on which the theme is based
"Quantiles",	// The method for creating the classes
8,	// Eight different classes are requested
{
{"Other", "True"},	// Include an Other class
{"Pretty", "True"},	// Round off the high and low values automatically
{"Force", 1000}	// Force a break in the classes at a value of 1000
})
t2 = CreateDotTheme("Population by Gender",	// The name of the theme
{"Male", "Female"},	// The fields on which the theme is based
25000,	// One dot represents 25,000 persons
null)	// No options for this example

// Show the color theme for all States...
RunMacro("set up styles for the first theme")	// See the next topic on theme styles
ShowTheme("States\|", t1)

// Show the dot-density theme only on the selection set...
RunMacro("set up styles for the second theme")	// See the next topic on theme styles
ShowTheme("States\|High Income", t2)

// Finally, redraw the map...
RedrawMap()
endMacro

For more information, see:

Getting Information about a Theme

Theme Styles