Defining Layers in Imported Data

In addition to identifying the default composites, a preliminary step of the import is to identify all of the layers that will be created by the import. Each layer represents a set of features on the map and how those features will be displayed. With the exception of the TIGER and DYNAMAP import types, which have a standard set of predefined layer definitions, the layer definitions are based on attributes that are found in the input data. The layers are actually created during the import. However, you can review the default layer definitions before the import takes place, and you can modify them if you choose.

Before clicking the Import button, you must fill out the INPUT and OUTPUT panes on the GIS Spatial Data Importing window. Then you can click the Modify Layers button, which opens the Modify Layers window as shown in the following display.

The Import Window for Defining Layers

When the window is first displayed, the first layer in the Layer Names list is selected and its definition is displayed in the window. This list contains all of the layers that will be created for the import. To review a layer, select its name in the Layer Names list. All of the information in the window will be updated for the selected layer. You can now modify any of the fields. Unlike the Import window for modifying composites, all the fields in the window, except the Layer Statement field, are immediately editable, and none are hidden. The following table describes each of the fields and their uses.

Import Window Elements for Modifying Layers

Window Elements	Use
Layer Names	Selectable list of layer names.
Reset Layer	Resets the layer definition to the way it was initially (with the exception of the layer name).
Name	To change the layer name, type another name in this field.
Action	Choices are either Create or Replace.
Type	Specifies the type of layer to be created or replaced. Choices are Point, Line, or Area. By default, one of these will be selected, but you can change it to either of the others.
Description	A description for the layer.
On/Off Scale	Defines the scale at which to turn the layer on and off. The default is 0.
Where Expression	Specifies the expression to be used to define features for the layer. You can type directly in this field. Invalid expressions are flagged.
Where Builder	Brings up the WHERE window, which enables you to build a valid WHERE expression. When the WHERE window is closed, the resulting expression is displayed in the Where Expression field.
Clear Expression	Clears the WHERE expression.
Composite Variables	Contains all the composites that are defined for this import. Selecting a composite inserts it in the LAYER statement.
Layer Statement	A noneditable text field that displays the LAYER statement as it will appear when it is sent to the GIS procedure by the import.

The command buttons are used to perform window-wide functions. The Close button closes the window and saves all changes that you made. The Cancel button closes the window and cancels all changes that you made. The New button allows a new layer to be defined. The Remove button removes the currently selected layer. The Help button accesses the Help system.

After importing, you can use the GIS procedure to create additional composites and define new layers. For details, see The GIS Procedure.