Digitizing with MapInfo Pro is located on the SPATIAL tab, in the Edit group, by clicking Digitizer Setup.
Setting the Projection before Digitizing
When you digitize a paper map, you need to specify the projection used for that map, (Default Table Projection preference is used for this operation). Most paper maps indicate their projection, generally in the legend. You can use any of the projections MapInfo Pro provides, or you can create your own coordinate system.
When digitizing from an aerial photograph, you should generally use the Longitude/Latitude projection.
In order to digitize a non-earth map (such as a floor plan), the active Map window must be non-earth.
Clicking Projection in the Digitizer Setup dialog box opens the Choose Projection dialog box where you specify the projection of the paper map you are digitizing.
Setting Control Points before Digitizing
Once you have set your projection, you need to set control points. You set control points so that MapInfo Pro knows how to interpret the puck position. To set a control point, you indicate a position on the digitizer tablet by pressing a button on the puck. Then you type in the map coordinates that correspond to that point. MapInfo Pro determines the map values from these coordinates.
You should use at least four control points when digitizing a paper map. When you are digitizing from an aerial photograph, you might want to use thirty or more control points. MapInfo Pro allows you to create as many control points as you need. You do not need to have the map in any special orientation when you digitize. However, once you start digitizing, you should not move the map for the duration of the session. We recommend that you tape your map firmly to the tablet to make sure it does not move during digitizing.
When you choose four or more control points, MapInfo Pro makes an error calculation estimating the possible error in your setup.
Dealing With Error Estimates (Digitizing)
When you digitize a map and error values are high, the resulting map table may be too inaccurate for reliable use.
MapInfo Pro makes the error calculation by determining the relative positions of the control points based on the map coordinates you typed in. It can then determine where those points should be on the tablet. The error is the difference between where a point should be on the tablet and where you actually clicked. An error value displays for each point.
When you are digitizing from a paper map, these error values should be quite small; they should be on the same scale as the resolution of your digitizer. In most cases errors should be in thousandths or hundredths of an inch. Errors approaching a tenth of an inch are probably too large. When the error is too high, you should:
- Check the projection to make sure it matches the projection printed on the map. To do this, simply click on Projection in the Digitizer Setup dialog box. The Choose Projection dialog box displays with the current projection highlighted. If that is not the correct projection, scroll through the list and choose the correct projection.
Once you change the projection, MapInfo Pro recalculates the error.
When the problem is not with the projection or when changing the projection only slightly reduces the error, then you have to check individual control points. Start with the points with the highest error (choose Edit in the Digitizer Setup dialog box). Correct your control points until the error is acceptably small.
When you are digitizing from a photograph, you should use many control points, preferably over twenty. In general, the more control points you use, the smaller the error.
Setting Digitizer Buttons
Clicking Buttons in the Digitizer Setup dialog box opens the Set Digitizer Buttons dialog box where you configure the digitizer buttons.
If you have two or more buttons on your digitizer puck, you can designate which button performs each function.
- Click Buttons in the Digitizer Setup dialog box to open the Set Digitizer Buttons dialog box.
- Click the digitizer button you want to use for drawing objects (this sets the specified button as the drawing tool), another Set Digitizer Buttons dialog box opens.
- Click the digitizer button you want to use for completing polygons and polylines, your digitizer puck is configured to your specifications.
If your digitizer puck has only one button, you must use it for both drawing and completing polylines and polygons. In this case a single click enters a point when you are drawing an object. A double-click completes a polyline or polygon.
Configuring Digitizer Buttons
Specify which digitizer button is used to draw and which is used to close polygons and polylines. By default, MapInfo Pro assigns the first function to button one and the second function to button two. You can override the default if you want. Also, you can use one button to serve both functions. In this case, you single-click to specify a point and double-click to complete a polygon or polyline.