Geography Reference
In-Depth Information
Exercise 5-5 (Warm-Up)
Digitizing Geodatabase Polygons and Exploring Topology
Previously, in Exercise 5-4, you digitized lines and then converted them into polygons. The conversion
process took care of the topology issues of overlaps and gaps. You can also digitize polygons directly,
as you will see in this exercise, but then you have to cope with topology more directly. We look at some
examples first, examining two different ways of dealing with the topological problems that occur. Then, in
Exercise 5-7, you will digitize the polygon features of a newly discovered sixth island.
1.
Start ArcCatalog. In
___IGIS-Arc_
YourInitials
\Digitize&Transform
highlight the Catalog entry UTM_Zone_2, in Islands.mdb. Choose File > New > Feature Class.
Type Small_Squares for the name of the new Feature Class. Set the Type of features stored in
this feature class drop-down to Polygon Features. Click Next and then click Finish.
You are going to make a square 3 meters on a side as one polygon. Within it you will make a
square 1 meter on a side.
2.
Launch ArcMap with a Blank Map. Add Small_Squares as data. Click Start Editing. Within
the Create Features window, the template should be Small Squares. Select Polygon from the
Construction Tools. Move the crosshairs onto the map. Right-click. Pick Absolute X,Y from the
menu. Type 500000 for X and 6200000 for Y to make the beginning vertex. Press Enter.
3.
Right-click and pick Delta X, Y, which will let you provide relative coordinates for the next vertex.
Type 3 for X and 0 for Y. Press Enter.
4.
At this point all you will see is a red dot. The problem is one of extent. Choose the Zoom
In tool on the Tools toolbar. Repeatedly drag a small box around the red square until you see
a line of reasonable length. Click again on Small_Squares in the Create Features window to
continue editing.
5.
Make the third vertex: this time, use Ctrl-D to bring up the Delta X,Y window, type 0 for X and 3
for Y. Press Enter.
In this digitizing process, the software understands that you are making polygons (because
that is the type of feature you set up when you made the feature class), so the lines will
automatically close to form a polygon. Thus, you will see a polygon outlined in the sketch.
(Problems? If things are going wrong during the construction of a sketch, you can press
Ctrl-Delete on the keyboard to delete the entire sketch. To delete a particular vertex, click the
Edit tool (leftmost button on the Editor toolbar), place it over the vertex, right-click, and choose
Delete Vertex.)
6.
Make the last vertex: -3 (that's negative 3) for X and 0 for Y. Right-click and select Finish
Sketch, then Zoom To Layer. Save your edits. Open and resize the Small_Squares attribute table
and considering docking it.
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