QGIS User Guide - OSGeo Download Server

Understanding the new generation symbology
5.4 Proprietà dei layer vettoriali
There are three types of symbols: marker symbols (for points), line symbols and fill symbols (for
polygons). Symbols can consist of one or more symbol layers. It is possible to define the color of a
symbol and this color is then defined for all symbol layers. Some layers may have the color locked -
for those the color can not be altered. This is useful when you define the color of a multilayer symbol.
Similarly, it is possible to define the width for line symbols, as well as size and angle for marker
symbols.
Available symbol layer types
• Simple marker: Rendering with one of hardcoded markers.
• Simple line: Usual rendering of a line (with specified width, color and pen style)
• Simple fill: Usual rendering of a polygon (with defined fill color, fill pattern and outline)
• SVG marker: Rendering with a SVG picture
• Marker line: A line rendered by repeating a marker symbol
Color ramps
Color ramps are used to define a range of colors that can be used during the creation of renderers.
The symbol’s color will be set from the color ramp. There are two types of color ramps:
Styles
• Gradient: Linear gradient from one color to some other.
• random: Randomly generated colors from a specified area of color space
A style groups a set of various symbols and color ramps. You can define your prefered or frequently
used symbols, and can use it without having to recreate it everytime. Style items (symbols and color
ramps) have always a name by which they can be queried from the style. There is one default style
in QGIS (modifiable) and the user can add further styles.
Renderers
The renderer is responsible for drawing a feature together with the correct symbol. There are three
types of renderers: single symbol, categorized (called unique color in the old symbology), and
graduated. There is no continuous color renderer, because it is in fact only a special case of the
graduated renderer. The categorized and graduated renderer can be created by specifying a symbol
and a color ramp - they will set the colors for symbols appropriately.
QGIS 1.4.0 User Guide 51