Below is an example showing how to use the Screen Digiting Wizard to digitize lines in a shapefile. After pressing the OK button in the wizard's last panel, a Line Digitizing Menu opens for digitizing the lines in the shapefile. Other types of Line Digitizing Menus are possible, depending on whether key field values are to be manually entered or selected from a table. This decision is made in the wizard and will determine the type of menu used to digitize the lines.
How does the Key Field identify features?
How are lines structured?
A line digitizing menu appears when you are finished setting up the theme and you press the OK button in the wizard's last panel. In the example below, notice the menu indicates that the key field (MyLine_Id) is unique. To digitize a new line, enter a MyLine_Id in the menu and then use the Add tool. The MyLine_Id value you enter must be unique, otherwise the Add tool won't add the line. There are other tools for moving, splitting, and deleting lines, as well as for changing their key field values while preserving uniqueness.
Buttons Find Opens a menu for finding a line according to its key field value Undo Undo last screen digitizing edit Undo All Undo all screen digitizing edits since last save Tools Identify Provides information about the line you click Add Adds a line and assigns it the key field value entered in the menu Delete Opens a menu that prompts to delete the line selected with this tool. Drag a rectangle to select the line. When screen digitizing multi-part lines, you can drag a rectangle over just one part to delete just that part or all parts in the feature. Move Moves a line (overlapping lines only) Split Splits lines (unique and not unique lines only) Change Key Field Opens a menu that prompts you to change the key field value of a line you selected with this tool. Drag a rectangle to select the line. When screen digitizing multi-part lines, you can drag a rectangle over just one part to change the key of just that part or all parts in the feature. Markers Draws temporary markers for planning where to digitize
About Unique Key Fields
If the key field is unique, the Add, Split and Change Key Field tools enforce uniqueness and always prompt for values that are not already in the shapefile. This requirement is strictly enforced if the line structure is segment (as opposed to overlap) and you've added a line that intersects other lines. The new line splits the other lines into segments and consequently splits itself into segments. The Add tool prompts for unique key values for each of these segments.
Below are examples of the other types of line digitizing menus that the wizard makes possible. They offer different ways of assigning key field values to lines that are added to the shapefile as you screen digitize.
Enter or Select -
Enter a key field value or select one already in the shapefile and then digitize the line.
Lookup Table -
Select a record in a data table and then digitiz the new line.
The following examples illustrate what happens when you use the Add tool in the Line Digitizing Menu to add new lines under different setup conditions specified in the wizard. A single line is added in each example, but the results differ depending on whether key field values are unique or not unique, whether single or multi-part lines are desired, and whether or not lines overlap or intersect. Each example shows what the lines would look like in the view before and after adding the new one. Also, each one includes the resulting table records, which highlights some of the differences in screen digitizing overlapping, intersecting, single, and multi-part lines.
Unique key field values assigned to Overlapping lines:
Add line 1
Add line 3
Add line 89
Not Unique key field values assigned to Overlapping lines:
Add line 1
Unique key field values assigned to intersecting lines (Segments):
Add line 3 (splits line1 and 3 into 1, 3, 26, and 65)
Not Unique key field values assigned to intersecting lines (Segments):
Add line 3 (splits line 1 and line 3 into 1,3,3,1)
Unique key field values assigned to Multi-Part lines that Overlap:
Add a part to line 1