Exercise 1b: Digitizing lines and snapping
About digitizing with snapping
In the first exercise, you digitized a point over an aerial photograph; in this one, you will trace over the image to create a new line representing a road.
Because part of the road has already been created, you should use snapping to help ensure the new road feature connects to the existing roads. When snapping is turned on, your pointer will jump, or snap to, edges, vertices, and other geometric elements when it is near them. This enables you to position a feature easily in relation to the locations of other features. All the settings you need to work with snapping are located on the Snapping toolbar.
This exercise requires an active Internet connection since it uses imagery served from the Web. If you do not have an Internet connection or if the imagery is loading slowly, you can still perform the tutorial using an image that is installed with the tutorial data. You need to turn on the DOQQ imagery (local) layer in the table of contents, then you can turn off the World imagery (Web) layer.
Setting options for snapping
The Exercise1.mxd is open and you are in an edit session.
- Navigate to the Digitizing roads bookmark. The extent is just south of the point feature you created in the previous exercise.
- Add the Snapping toolbar to ArcMap. You can add a toolbar by clicking the Customize menu, pointing to Toolbars, then clicking the toolbar's name in the list. You can also add the Snapping toolbar by clicking the Editor menu, pointing to Snapping, the clicking Snapping Toolbar.
- On the Snapping toolbar, click the Snapping menu and confirm that Use Snapping is checked. If it is already checked, do not click it again, since that will turn off snapping. If Use Snapping is not checked, click it to enable snapping.
- Look on the Snapping toolbar and confirm that End , Vertex , and Edge snapping types are active. When enabled, the buttons are highlighted. If they are not enabled, click each button to enable those agents.
- Click the Snapping menu and click Options. From this dialog box, you can specify settings for snapping in ArcMap.
- Ensure the snap tolerance is at least 10 pixels.
Check the boxes for Show Tips, Layer Name, Snap Type, and Background. Most likely, you only need to check on Background, as the others are turned on by default. A SnapTip is a small piece of text that pops up to indicate the layer you are snapped to and with which snap type (edge, end, vertex, and so on). The background is useful to help you see the SnapTip when working over an image.
- Optionally, you can change the color used for the snap symbol and set SnapTip display options, such as the size or font of the tip.
- Click OK to close the Snapping Options dialog box.
Digitizing a line
You are now ready to begin digitizing the new road. In the Create Features window, click the Local road line template, which is grouped under Roads. This feature template was created for you and saved in the tutorial map document.
The list of available construction tools at the bottom of the window changes to those used to create lines. Since the Line tool is the default tool for this template, it is activated automatically.
- Rest your pointer over the endpoint of the existing line in the western portion of the map display, but do not click yet. Notice that the pointer icon changes to a square snap symbol and a SnapTip appears with the name of the layer (Roads) and the snap type (Endpoint) in use. You can zoom or pan closer if you need to do so.
Using the aerial photo as a guide, digitize the new line by clicking the map each place you want to add a vertex.
- Once you have digitized the new line, snap to the end of the existing feature and click to place a vertex there.
- Press the F2 key, which finishes the sketch to turn your shape into an actual feature in the geodatabase. You can finish a sketch in one of several ways: pressing F2, double-clicking, or using the right-click shortcut menu or the pop-up Feature Construction toolbar.
- To continue to the next exercise, click Exercise 1c: Creating new feature templates.
In this exercise, you learned how to set up snapping and use it to help you digitize a new road that connects to existing roads.