Point Digitizing

Below is an example showing how to use the Screen Digiting Wizard to digitize a point shapefile of wells. After pressing the OK button in the wizard's last panel, a Point Digitizing Menu opens for digitizing the points in the wells shapefile. Other types of Point Digitizing Menus are possible, depending on whether key field values are to be manually entered, selected from a table, or automatically incremented. This decision is made in the wizard and will determine the type of menu used for point digitizing.

Screen Digitizing Wizard

  1. Specify the Key Field in the first wizard panel. If you need to know the values already in the key field you have chosen, use the List Values check box to display them in the menu. This is a read only list for reference purposes.

  2. In the second panel, specify how the key field identifies features in the shapefile. For point shapefiles, there are two options - Unique or Not Unique. Unique only allows you to add points with key field values that are not already in the shapefile. All points are uniquely identified. Not Unique allows you to add more than one point with the same key field value (duplicates allowed). In the example below, the key field is unique. This is the default setup for points.

  3. In the third panel, indicate how you want to specify key field values when digitizing. There are four options for points. You can (1) enter the value, (2) enter a (new) value or select from values already in the shapefile, (3) select values from records in a lookup table, or (4) have ArcView auto number and assign the point the next highest value in the shapefile. The Enter Value option was chosen in the example below, which is the default setup for points.

  4. In the fourth panel, indicate whether you want Arcview to index the key field and shape field. The wizard reads the shapefile to determine whether these fields are indexed and displays their state in the check boxes. If they are checked, the fields are indexed. Unchecking them removes the index and checking them adds the index. Additionally, you can specify an appropriate scale range for screen digitizing if the view's map units are set in advance. This is optional. If you specify a scale range, the screen digitizing menu will be usable only when viewing within this range. This scale range does not affect the theme's display scale range. Below the screen digitize scale range is set for viewing between 1:6,000 and 1:24,000 scale.

Point Digitizing Menu

A point digitizing menu appears when you are finished setting up the theme and you press the OK button in the wizard's last panel. The example below is for screen digitizing points in the Wells theme. Notice the menu indicates the key field (Well_Id) is unique. To digitize a new well, enter a Well_Id in the menu and use the Add tool to digitize the point location. The Well_Id must be unique, otherwise the Add tool won't add the point. There are other tools for moving and deleting points, as well as for changing their key field values while preserving uniqueness.

Buttons
Find Opens a menu for finding a point 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 point you click
Add Adds a point and assigns it the key field value entered in the menu
Delete Opens a menu that prompts to delete points selected with the tool
Change Key Field Opens a menu for changing the key field value of the point clicked on
Markers Draws temporary markers for planning where to digitize

Display cross hairs

On occasion you might want to line up the mouse pointer with other features in the view to determine where to add a new point. Say, for example, the point is directly east of a road intersection. As an option, you can momentarily display long cross hairs just before adding, moving, or deleting a point. Just hold down the Shift key when using the Add, Move, Delete, and Change Key Field tools to display a cross hair for one second. If you want to use cross hairs when adding a point, keep holding down the Shift key and move and click on the mouse until you have it in the correct location. Once you have the mouse pointer positioned at the correct location, add the new point by clicking on the mouse again without holding down the Shift key.

Other Point Digizing Menus

Below are examples of the other types of point digitizing menus that the wizard makes possible. They offer different ways of assigning key field values to points 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 point.

Lookup Table -

Select a record in a data table and then digitiz the new point.

Auto number -

Automatically assign a unique key field value to each added point. ArcView assigns it the next highest value in the shapefile. This approach is commonly referred to as auto number or auto increment.