Registering a paper map for digitizing
Before you can start digitizing, you must register your paper map into real-world coordinates. This allows you to digitize features directly in geographic space. Always register your map at the start of each digitizing session, even if this means registering the same map more than once. Your paper map might shift between sessions; reregistering helps ensure that your digitizing is accurate.
The Digitizer tab on the Editing Options dialog box displays the current x,y location of the digitizer puck on the tablet. The coordinates change as you move the puck along the tablet surface. This helps orient you to the location you're digitizing.
When registering your map, you have the option of saving the ground coordinates you entered for later use—for example, if you want to reregister your map or register another map that uses the same control points. These ground coordinates are stored in text files.
- Click the Editor menu and click Options.
- Click the Digitizer tab.
If this is the first time you have registered the map, perform the following:
- With the digitizer puck, digitize the control points you established earlier on your paper map (with the puck over each control point on the map, press the button you configured to perform a mouse click). A record appears in the X Digitizer and Y Digitizer columns for each control point you digitized.
Type the actual ground coordinates for each control point in the X Map and Y Map fields. An error in map units is displayed at each control point. A root mean square (RMS) error is displayed in map units and in digitizer inches.
If you want to remove all the ground coordinate records and start over, click Clear on the Digitizer tab. To remove an individual record, click the number in the Point column corresponding to the coordinates you want to remove and press Delete.
- Optionally, click Save to save the ground coordinate values for future use.
You can also register the map by loading control points from a text file.
- Click Load.
- Navigate to the file you want to use and click Open.
- Click the first record and digitize the first control point with the digitizer puck. The ground coordinates appear under the X Map and Y Map fields.
- Digitize each of the other control points and note the RMS error.
- Click OK to register the map.
If you installed ArcGIS before installing your digitizer, the Digitizer tab may be missing. To add the tab, you must register the digitizer.dll file. When you restart ArcMap, the Editing Options dialog box will have the Digitizer tab.