An Orbit Legend is a description of how a dataset must be graphically drawn. A legend definition contains all required information to allow the Orbit system to draw all data in a single dataset. A legend is thus associated with one specific dataset.

Legends are associated with datasets in different ways : a default legend, a user choice, a workspace setting, an edited legend, format-specific parameters, default Orbit drawing parameters. Read on about how to associate legends with datasets.

In Orbit GIS, one can use the Legend Editor to load, save, reset and edit a legend.

Remember : A single legend file is always associated with a single dataset.

Use a single legend file per dataset. You may wish to define different legends related to a dataset to define different presentations of the data. Only one legend can be activated at the time.

As datasets consist out of Models, so do Legend files. To be technically exact, a legend is defined per Model, as the Model contains the data definitions. A Legend File holds the individual legends for each Model within the dataset. Read more about this in Understanding Orbit Datastructures.

Each of the four major types of spatial components (Point, Line, Area, Image) allow obvious different drawing parameters. The legend is logically adjusted to each type. Using the Legend Editor, the appropriate parameters will be presented for editing.

If you wish to define a conditional legend, e.g. color range based on a classification, Orbit allows to use any attribute field. Conditional settings are called classifications. You can define a classification based on any attribute for each graphic parameter.

As the legend defines how a dataset is drawn, it is useful to have that information listed in the Dataset List. The more complex your legend definition gets (classifications), the more complex the display of all classes gets. The Legend Editor presents a special tab to adjust the legend display.

Use the Dataset menu to alter visibility of the Legend Display in the Dataset List :

The Orbit Engine is capable of using very complex legends. It exceeds the capabilities of the Orbit GIS Legend Editor.

As specialized user, you will be able to define a legend far more complex than editable through the Legend Editor window. The Legend file is an ASCII file, editable in every simple word processor, such as 'Notepad' or 'vi'. You can learn more about the legend file, and how to manually create one, on the Orbit web site.

When opening a complex legend in the Legend Editor, the editor will display a warning. You can edit the legend, and apply the changes. However, you should not save the legend as the complex definitions will be lost.

Complexity not supported in this Legend Editor concern mainly the capability of using multiple-attribute queries per graphic parameter, automatically generated layouts, and manually defined legend display lists. Consult the legend file OLG documentation for detailed descriptions.

An Orbit Legend can apply to any type of resource. The legend can be created manually (by editing the legend file in a text editor) or by using the Legend Editor, a part of the Dataset Properties window.

The legend is stored in a file with extension 'olg', meaning 'Orbit Legend File'. A default legend file is recognized and automatically associated with a resource if the filename is equal :
<filename>.<supported format extension> and <filename>.olg . Both files must reside in the same directory.

When saving a Workspace, the at that time associated legend file is automatically linked in the workspace file. Opening a workspace will try to load that legend file.

The Orbit GIS Workspace saves the current Legend File name in use, if any. This legend file specification overrides the default associated legend file. Simply save the workspace. Remember to save the legend file first, as the Workspace does not save legend file and definition itself, only the (relative) path to the file. Be sure to save the legend before saving the workspace. When no legend specification is available in the workspace, the default legend file is read and used, if it exists.

When no default legend file is available, the resource driver may extract graphic parameters from the resource. Some storage formats store values for graphic representation of the data in the data file, as do some CAD-oriented formats. Depending on the implementation of the resource driver, the driver may support these parameters. Refer to the Resource Driver implementation sheets for details on each storage format.

If no graphic information is available, Orbit GIS will draw the data using its default settings, assigning random colors and symbols.