Digitizing in ArcView
Preparing your paper map for digitizing
-Your map should be reliable, up-to-date, and in fairly descent shape (not torn, over-folded etc.).
-If your map has a grid or a set of known ground points, you can use these as your control points (tics). If not, choose at least four distinctive locations such as road intersections, and mark them on your map with pencil. Give them each one unique number and write down its actual ground coordinates. The more tics you identify, the more accurate your digitizing will be. You will use these tics to register your map in geographic space.
-Place your map on the tablet and attach it with masking tape. Donít worry about aligning the map precisely on the tablet. ArcView corrects any alignment problems when you register the map and tells you about such adjustments in the error report.
Loading the Digitizer extension
Open ArcView by double clicking the icon on the desktop.
Make the Project window active (upper left). Open new project or open existing project.
From the File menu, choose Extensions.
In the Extensions dialog, click on the box next to the Digitizer extension.
Preparing the view you will be digitizing into
Create a new view or open an existing view you wish to digitize into (double click view icon, or desired view)
You now have to prepare your view for digitizing by specifying the projection used by the paper map you are about to digitize from.
From the View menu, choose properties.
In the dialog that appears, click the Projection button.
In the dialog that appears, set the projection used by the paper map you will be digitizing. If necessary, set the custom projection parameters to match your paper mapís parameters.
Set the desired Map Units from the dropdown list. By default, the map units are meters.
-When you digitize features, ArcView will automatically convert their coordinates, store them in decimal degrees, and display them in your view using the projection you specified.
Registering your map
In order to digitize features from your map, you must register your map into geographic space. You do this by telling ArcView the ground coordinates for your tics identified while preparing your map.
To register your map for the first time: From the view menu, choose digitizer setup. If the menu does not have the digitizer setup then you have forgotten to load the Digitizer Extension.
In the dialog that appears, specify how much error you will allow by entering a value into the Error Limit field. The default value is0.004 inches.
Click the digitizer puck icon and then using the digitizing tablet, digitize the tics you identified on the paper map (if in Lat/Long, they cannot be in Deg/Min/Sec they must be in decimal form, a converter for this can be found in e:\Gis\Gis-Misc\Non-Arcview Gis documents/Lat Long conversion). Digitize the tics by holding the cross hair over the point and clicking the 0-button on the puck. Continue this for all your tics.
Type the actual ground coordinates for the tics in the X coordinate and Y coordinate fields for each associated tic entered in.
Once you entered the minimum four tics and their true coordinates, ArcView will display the error for each tic entered. It also calculates the Root Mean Square error and displays the information as calculated error.
Compare the calculated error with the value specified in the Error Limit edit box. It should be lower than the Error Limit. If the calculated error is larger than the Error Limit, you cannot register your map, and you will have to do one of the following:
Re-digitize tics on your paper map.
Re-enter the corresponding ground coordinates by reselecting the points on the screen or typing in the values again.
Increase the value in the Error Limit field so that the new value is larger than the calculated error (press the TAB key to accept the new value). Substantially increasing the error tolerance may lead to poor quality digitizing.
Optionally, you can click the Save button and save the ground coordinate values for future use (be sure and remember where you saved them at).
Click on Register button. This will register your map.
Note: Register your map at the start of each digitizing session!
How to digitize features
Configuration of Puck:
Button 0: single left mouse click
Button 1: double left mouse click
Button 2: single right mouse click
Button 3: double right mouse click
Creating a New Theme to be digitized:
From the View menu, choose New Theme.
Select desired Theme you wish to digitize (point, line, polygon), only one type of Theme can be digitized into a single .shp file (if you have lines and polygons to do, then you will have to make two new themes).
Define where you wish to save the theme file to ( I recommend putting it in the same place as your project is located in).
Click on desired theme you want to digitize into.
From the Theme menu, choose Start Editing. (or if it is not available then you are already in edit mode and can begin to digitize your features).
Example for polygon digitizing:
Using the mouse, click on the graphic tool (small black dot on lower right hand side of tool icons), hold left button down a drag down to Polygon tool.
Place the puck on the paper map and begin to digitize the polygons, this can be done by starting the polygon with a node (click button-0),tracing the polygon with any number of vertices ( clicking button-0), and ending the polygon with a node (click button-1).
Your polygon should now be drawn on the View screen.
Begin to draw a new polygon.
After digitizing select Stop Editing from the Theme menu, and save your edits.
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