Geographic and Attribute Data: Selection, Input, and Editing - Introducing Geographic Information Systems with ArcGIS - page 333

When you create polygons, you see a closed figure after you have put in the first three vertices. To
complete the figure, double-click the last vertex, or single-click the last vertex and press F2 to complete
the sketch. The polygon will automatically close.
5. If necessary, rearrange the entries in the T/C so that MSH is again at the top of the list and
the image is visible. Digitize the cauldron of the volcano. There appear to be several lakes (they
appear black on the orthophoto) on the island; zoom in and digitize them. Digitize what appears
to be new lava flow that covers about a third of the island, and in some cases, runs down to
the ocean. Click Save Edits. Click Stop Editing. Turn off the image layer MSH. Make the North_
Islands_Polygons layer hollow so you will be sure to see the boundaries of all the polygons. The
map of the newly digitized island should roughly resemble Figure 5-15. Save edits. Stop editing.
Save the map as North_Islands_map4 in your Digitize&Transform folder. Launch the ArcCatalog
sidebar.
From this point on in the exercise, the instructions will become very general. You should use the tools you
learned in the previous exercise to accomplish the tasks.
6. Using ArcCatalog, make two copies of North_Islands_Polygons in the same dataset that you
have been using.
7. In ArcMap, use clip operations on one copy to make separate polygons of the lava flow, the
lakes, and the cauldron. Since polygons are nested within polygons that are themselves nested
this can be a little tricky. Things will probably go better if you so two things: (1) start with the
most deeply nested (smallest) polygon first, and (2) open the attribute table and use it to select
the polygons, rather than relying on selecting them graphically.
8. Merge the cauldron into the Seismic Group.
9. Merge the lava flow area with the Safety Board.
10. The lakes go to the Aqua Board.
11. The remaining land area goes to the East County.
12. Save edits and remove the first copy of North_Islands_Polygons from ArcMap. Add the second
copy of North_Islands_Polygons to ArcMap. Close ArcMap so you can make topology with
ArcCatalog.
13. Use topology on the second copy. Perform the same merging operations as immediately above.
14. Not that you ever make errors, but if you had merged the polygons that should not be
merged, what toolbar and tool would you use to separate them again? ___________________,
___________________.
Creating a 3-D Feature
15. If you happen to have dismissed ArcMap, start it again with North_Islands_map4. Turn on the
image layer MSH. Zoom in on the sixth island. You should see the image of the volcano. (If not,
you will have to Georeference the image again.)