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Click on PC or MAC to download the Data Set for this lab. PC (96 K) MAC (128 K) Digitizing and Data Automation Geographic Regions. The region is one of the major spatial building blocks of GIS. Regions can be represented as vector polygons or raster clusters. Regionalizations are of great interest partially because there is generally disagreement on what the boundaries, extents and locations of many regions actually are. This has led to a great deal of research and commentary both on the nature of regions and the techniques for defining them. In this lab you will create a regionalization of the United States based on your own understanding of the divisions that are present within the country. Creating New Spatial Data by Digitizing. Digitizing is the process of copying an existing map to create a digital version of the map. During the digitizing process, maps can be selectively digitized and generalized to create a simplified version of the original. Digitizing can be performed either using a digitizing tablet to copy a paper map or using ìheads-upî digitizing which involves digitizing from an existing digital data set on screen. We will be doing ìheads-upî digitizing in this lab. We will set up our newly digitized theme as a shapefile, and edit the table to make each polygon a unique unit.
Task Set 1
Task Set 1: Digitizing in ArcView This lab will differ from previous labs in that there will be fewer questions for you to answer, and a more difficult mapping assignment for you to turn in. Be aware that good digitizing takes concentration and time; plan accordingly. Start ArcView, set your working directory, and open the States.shp theme from the esri/esridata/usa data set. Use the Legend Editor to set the Legend Type to Single Symbol. Make sure to make the theme visible. You will use this theme as the template for your own digitizing. When digitizing in ArcView, you must digitize into some predefined geographic space such as the states theme. You should now be looking an ArcView window with a map of the United States including Alaska and Hawaii. Now clip out the lower forty-eight states. Use the Select Feature tool to drag a box around the lower forty-eight states.
The selected states should turn yellow.
Now pull down the Theme menu and select Convert to Shapefile. Name the new theme lower48. Delete the States.shp theme and make lower48.shp visible. Use the Zoom to Full Extent button to center the map in the view. Now we need to prepare for digitizing. Pull down the View menu and select New ThemeÖ
When the New Theme window pops up, name the new layer "Regions.shp".
Notice the dotted line around the check box of Regions.shp. This dotted line will appear when a theme is active for editing. Now we will practice digitizing. Find the Draw tool in the lower menu bar. This tool can be extended by clicking on it. You should see a column of nine Draw tools. Notice that only the polygon tools are active. This is because your new theme is a polygon theme. When you select one of the tools, it will appear as the top icon in the column. Select the Draw Polygon tool and draw a large polygon by left clicking in the view window. To end the polygon, double left click.
If you make an error in digitizing you can back up one point at a time by right clicking with the mouse. The digitizing options window will pop up. It allows you to do simple editing as well as panning and zooming. Experiment with this window. You will need it.
Now select the Append Polygon tool. Left click inside the polygon you just drew, and then draw a polygon adjacent to your original polygon. End by double left clicking inside the first polygon.
The second polygon should automatically append. Select the Split Polygon tool and draw a line across the first polygon, double left clicking to close. You should now have three polygons. Go to the Theme menu, select Stop Editing and save your work.
Print this practice drawing and turn in with your lab.
Question: If you digitize into a reference map in the geographic co-ordinate stucture, what will be the projection of your newly digitized map?
Now that you
have practiced with the digitizing tools you will create a regionalization of
the United States. The digitizing in the exercise will consist of two problems.
The first will be copying the relatively fine line work of the continental coastline.
You do not need to digitize islands. The other will consist of creating
more general internal boundaries around regions.
Your assignment in this exercise is to regionalize the lower 48 states of the U.S. into at least 5 regions. These regions can be based on any concept you have of the U.S., with the proviso that you MAY NOT use any existing state boundaries. Create a new theme, View->New Theme, and name it. Make sure that your new theme is active. Digitize your new regions. If you do not complete your work in one session you will need to save your edits, and select Theme->Stop Editing. Be certain that the project is saved to your own home directory. When you return to work, open the project, make your new layer active and select Theme->Start Editing. You may then continue your digitizing project. When you are finished, set your new theme to no fill. You should see only lines. Make the line a dark contrast to the polygons underneath. Zoom in on the coast of Maine so that your lines and the original lines are clearly visible. The quality of your linework on the coasts is important. Print and turn this map in with your lab.
Zoom out to the active theme. Print and turn your regionalization in with your lab.
Question: If you decide to use the legend editor to change the legend type of your new layer to Unique Value, what happens?
Task Set 3:Creating a Table and Entering Data
Now we will work with the table for the new regions theme to build a simple database, and make each object unique. Make your theme Myregions.shp active. Use the Open Theme Table icon to open the table.
Question: Draw the table for Myregions.shp. How does this table differ from other tables you have seen? Can you explain why this might be?
Set the fill symbol for Myregions.shp to a solid color. This will make it possible for you to work interactively between the table and the view. Using the table editing tool, assign each record a unique number. Add a field named "Name".
Select each record, one at a time. The polygon that corresponds to the record should become highlighted. Check which region it should be and edit the Name field for the record with the correct name.
Save the table and stop editing. Now select the Legend Editor, and select Unique Value as the Legend Type. Set Values Field to Name. Click Apply.
Now with no polygons selected, use Theme->Auto-label to label your map. You may use either the ID or the Name as the Label field.
Select an appropriate projection, and project your map. Use layout to create a map composition. The map should include at least a legend, a title, and a neatline. Print and turn in this map with your lab.
Question: Discuss the validity of the region concept. Do you think regions exist? Were you uncertain of where certain boundaries ought to be?
Question: Look at another studentís map. Does it seem as accurate in the interpretations of regions as yours does? Why or why not?
In
this lab you have digitized a new theme, created a useful table, used an auto-labeling
algorithm, and created a final map composition. In addition you have created a regionalization
of the United States based on your own personal knowledge. This should have given you the opportunity
to reflect on the concepts of regions, and the wide variety of views that
individuals might have of regions and their creation.
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