GIS Lab Exercise #3 - Digitizing Data in Arc/Info

by
Thad Tilton
Department of Geography and Earth Resources
Utah State University
Logan, UT 84322-5240
ttilton@geog.usu.edu
 

This exercise will briefly introduce you to the methods of inputing geographic data into Arc/Info. Data may be input by drawing with the mouse, by entering geographic coordinates from the keyboard, or by using the digitizing tablet to 'trace' the desired coverage into digital form.

 

  Digitizing in ArcEdit

With the exception of the generate command, all digitizing with Arc/Info is done in the ArcEdit sub-program. To get to this sub-program, type arcedit at the arc prompt.
The following is a list of commands that you will need for most digitizing sessions in ArcEdit ... 
NOTE: Additional fields within < > are required, those within
{  } are optional.

Arcedit: display   <9999>   {2,3} Arcedit: create   <out_cover>   {tic_bnd_cover} Arcedit: editcover   <cover> Arcedit: editfeature   <feature> Arcedit: mapextent   <cover> Arcedit: backcoverage   <cover>   {symbol} Arcedit: backenvironment   <feature>   {on,off} Arcedit: drawenvironment   <feature>   {on,off} Arcedit: image  <image> Arcedit: draw  
The above commands are used to set up your digitizing session. Once you have your edit coverage and any backcoverages drawn as you've specified, you can start digitizing with the mouse or the digitizing tablet.

  

Assignment

Make sure you are in your gis# workspace, then follow through the ArcEdit session below by typing the following commands...
At the Arc prompt, type arcedit

you will get an Arcedit prompt, type the following commands as shown ...

Arcedit:  create mouse /auto/gisclass/cachebnd Arcedit:  mape mouse
Arcedit:  display  9999
Arcedit:  editcoverage mouse
Arcedit:  backcoverage /auto/gisclass/roads 2 Arcedit:  backenvironment arc Arcedit:  drawenvironment all
Arcedit:  draw
Arcedit:  backcoverage /auto/gisclass/roads 3
Arcedit:  draw
Stay in your digitizing session, we will be working more with it in a bit ...


  


Adding Features with the Mouse ...

Assuming that the editfeature has been specified, when you
type add, you will get one of the following menus....
 

  

Assignment

Continue following along by typing the commands below ...
 
Arcedit: editfeature arc
Arcedit: add
Try adding a few arcs, experiment with the various menu options. With your cursor in the display window, press 9 when you are done adding arcs.
Arcedit:  editfeature point
Arcedit:  add
Add at least 10 points, experiment with the various menu options.
with your cursor in the display window, type 8 (digitizing options) from the keyboard. This will give you a new list of options.

             With your mouse cursor in the display window, Press 9 on the keyboard to quit adding points.
Arcedit:  quit
 
 

Once you quit Arcedit, you will return to an Arc prompt. You should now have the coverage named mouse in your workspace that contains several lines and points that you added with the mouse.

To complete the first part of this assignment, find the command that will write the points in your coverage to a text file of X and Y coordinates (Hint: it is an Arc command and is the opposite of generate). Perform the command, and mail me the text file of coordinates  (gisclass@geog.usu.edu)

  
 
 

Using the Digitizing Tablet

 

Digitizing with the tablet is also performed in ArcEdit. You will use the same commands shown above to set up your digitizing session. The only difference is that you will have to coordinate the digitizing tablet to the map you are working on. Below are some additional commands that you will need to do this ...

Arcedit:  digitizer   <95000>   </dev/ttya>
Arcedit:  &station <digitizer>
Arcedit:  create  <cover>   {tic_cover}
Arcedit:  coordinate <digitizer>  {cover}
Arcedit:  coordinate   <mouse  |  digitizer>

Defining Tics for a New Coverage...

When you create a new coverage to be digitized from the tablet, you will get the following prompt and menu, asking you to define at least 4 tics.

 

You should find and mark your tic locations on your map before you begin digitizing. Enter tics by placing the crosshairs on the "puck" over the position on the map where you wish to place a tic. First enter the tic # from the keypad (usually, your first tic will be #1, your second #2, etc.), then enter "A" to give the position, and "A" again to enter. When you have entered a minimun of 4 tics, enter "0AA" from the puck to indicate you are done entering tics.

Each time you go into ArcEdit to digitize from the tablet, you will be prompted to enter these tics again to register your map to the GIS. Make sure you mark them so you can enter the same locations each time.

Digitizing is performed as with the mouse. Simply type add once your editfeature is specified and you will get one of the following menus ....

Points...

 

Arcs...

 


Move your crosshairs over the desired position and enter the appropriate number from the digitizing puck (2 for nodes, 1 for vertices, etc). When you are done adding features, select 9 from the puck to get the arcedit prompt back.


To quit your ArcEdit session, type quit. To quit Arc, type quit again at the arc prompt.


 

Assignment

Follow through the following digitizing session using the digitizing tablet and the Cache Ownership map provided ...

Arc:  arcedit
Arcedit:  &station dig
Arcedit:  create cache_own
Arcedit:  editfeature arc
Arcedit:   drawenvironment   all
Arcedit:   draw
Arcedit:  add
Digitize the ownership polygons for the portion of Cache County you were assigned. Make sure that everyone in your lab group gets a chance to digitize.
Arcedit:  quit
 

Arc:  quit 
to exit arc.

 
 
Getting back into your digitizing session:

Arc:  arcedit

Arcedit: ec  owner
or whatever the coverage you created is called

Arcedit:  &sta  dig
Arcedit:   drawenvironment    all
Arcedit:   draw
Arcedit:  coord   dig   owner
enter tics,  etc.
 
 To recieve credit for this portion of the exercise, I will simply check your directory to make sure your group has digitized this map.