Attach the paper map to your digitizing tablet using masking tape, drafting tape, or a special residue-free putty. Drafting tape looks like masking tape, but leaves less residue when it’s removed.

You must always register your paper map before you can begin digitizing from it. This involves establishing control points to register the paper map to the geographic space of your GIS data. If your map has a grid or a set of known ground points, you can use these as your control points. If not, choose four to 10 distinctive locations and mark them on your map with a pencil. Give each location a unique number and write down its actual ground coordinates. Control points can also be saved to and loaded from x,y coordinates stored in a comma-delimited text file.

In this example, the control points and their ground coordinates are identified for you on the paper map.

After you have digitized all the control points and typed their actual ground coordinates, the total root mean square (RMS) error is calculated and displayed in map and digitizer units. Your X and Y Digitizer and error values may be different from the ones in this example.

To maintain highly accurate data, your RMS error should be less than 0.004 digitizer units (often inches) or the equivalent scaled distance in map units—the ground units in which the coordinates are stored. You can see what the map units are and set the onscreen display units by clicking View, Data Frame Properties, then the General tab on the Data Frame Properties dialog box.

You can redigitize control points by selecting the point you want to replace from the list, then clicking your paper map to capture a new control point. Redigitizing points with large error values can help reduce the total RMS error.

You need to enable digitizing mode once you have registered your map. Enabling digitizing mode maps the location of the puck on the tablet to a specific location on the screen.