Working with symbols and colors

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Symbols are a class of objects that use the Windows graphics device interface (GDI) to render text and shapes. Most customized drawings can be handled by creating new kinds of symbols. There are several standard symbol objects that can be used to render points, lines, polygons, and text. These basic symbols are used to draw graphic elements, such as neatlines and north arrows, on a map or PageLayout.

The TextSymbol, is used to draw labels and other textual items. In the case of a graphic element, a symbol is set as a property of each element; however, layers are drawn with a renderer, which has one or more symbols associated with it. The size of a symbol is always specified in points (such as the width of a line), but the size of its geometry (such as the path of a line) is determined by the item it uses to draw. Most items, when created, have a default symbol; therefore, instead of creating a new symbol for every item, you can modify an existing one.

Color is used in many places in ArcGIS applications - in feature and graphics symbols, as properties set in renderers, and as properties of a raster image. The type of color model used in each of these circumstances varies. You may be familiar with the red, green, blue (RGB) color model, which is based on primary colors of light. For example, a window background can be defined using the RGB color model because display monitors are based on this model.

Color can be represented using a number of different models, which often reflect how colors are created in the real world. Another common way to represent color is modeled on the creation of colors by spot printing with cyan, magenta, yellow, and black (CMYK) inks mingled on paper to create new colors. A map that is ready for offset-press publication can have CMYK colors to match the printer's inks.