ArcView - Exercise 2
April 26, 2005
Note - this week's assignment is due Noon on Friday, April 29. Next week is finals week and you will need your time to concentrate on tests, not assignments.
Please feel free to begin this exercise early so that I am immediately available for answering questions and demonstrating details for procedures you have not before performed.
Today we will learn how to develop our own ArcView project, using existing shapefiles and data organized in tables. * indicates a paragraph of discussion or asides, (1) - and other numbers enclosed in ( ) - indicate items to which you should respond by sending me the answer or item specified.
*If you wish to learn more about geographic information systems than this brief introduction, the Department of Geography and Planning offers courses, ESRI offers online courses for a fee and I have several projects ready for students who wish to pursue independent study or a senior thesis in geological applications of GIS (something you will probably not find in Geography & Planning) in which you can learn by doing, by helping solve a scientific question (geomorphology, tectonics, geological hazards). End of commercial. Now for today's exercise.
First, use Access to generate a list of global earthquakes (you saved the database assembled 2 weeks ago as instructed - right?) with magnitudes greater than 4.9. As you saw last week, small earthquakes are numerous and can clutter the map, so we will use only earthquakes large enough to feel to a distance of 20 to 50 km. Organize your query as follows:
Longitude - Latitude - Magnitude - Depth - Year - Month - Day - Hour - Minute - Second
After saving the query, Export as text file with headings and tab delimited under a new file name. Remember where you stash this file, you will need it shortly.
Exit Access and open ArcView. Create a new project with a new view. After selecting "Yes" for adding data to this view, navigate to the ESRI folder and open the esridata subfolder. Open the "world" folder and select "country.shp" as the theme you are adding to your view.
Open the theme table. (1) What kind of information is available?
*Note that there are additional folders and many themes, most with names that tell you what they are. This may come in handy the next time you need to prepare a map for a report.
Information in this table can be used to generate a map showing population density. You did this last week for provinces of Central America.
Set up a layout that displays your global population density map. (2) Does this map truly represent how closely people live to one another, particularly in large countries? Explain briefly.
(3) Export this layout as a .jpg (do not forget including title and author on this image) and attach it to an email message addressed and sent to me. If you do not receive a response, see me or call me (x2860) because it means that email is not working - a problem that must be resolved before Final Project day.
*In general, when I modify or edit a shapefile obtained from a reliable source, I never mess around with the original. I generate and operate on a duplicate.
Make certain that no countries are selected ("Clear selected features"). Then, in the Theme menu, select "Convert to Shapefile." Navigate to a folder on your flash drive and then name the new shapefile (do not change the extension - the .shp - in the title) something descriptive but different - perhaps 'Nations.shp'. Add the new shapefile to your view. Then select the "Countries.shp" theme and go to the "Edit" menu - Delete themes (Yes) removes the Countries theme from your view. Not to worry, this theme is still in the folder where you found it, it has not disappeared from the electronic universe.
I suspect your map consists of black borders separating nations of a single color (no political comment at this time). You can Classify by Unique Value (country name) to once again generate a political map of many nations.
About this time I suggest "Save project as" (File menu). Save your project to your flash drive.
*Saving a project does not move the theme files to location where the project has been saved. The Project is the set of instructions to bring into a project, its views, tables and layouts, the information from all of the locations you use to build a project. If I open a theme from a CD-ROM, I will need to have that CD in the proper drive the next time I open that theme.
*It is often convenient to generate new
shapefiles that are subsets of a much larger shapefile. For example, if I
were doing research on the European Union I would:
(a) use the magnifying glass to bring just Europe into the
screen;
(b) hold down the Shift key while selecting nations of the EU
on the map;
(c) after all were selected, select "Convert to Shapefile"
(Theme menu) and save the new theme under the name EU.shp;
(d) add that theme to the view.
Bringing your own data into a view: minimize the View and you should see this dialog box:
Click Tables, then Add (the tab should appear) and navigate to the location where you saved the earthquakes file generated at the top of this page. Note file format - reset from .dbf (default) to text file - once you find you earthquakes tab-delimited file, add it to your project.
After successfully adding the table, open the View. Under the View menu, select "Add event theme." Select the table with the earthquake data, specify Longitude as the "X" and Latitude as the "Y" coordinate, then OK (or whatever). A new theme should appear in the column left of the map - check the display box and you should see lots of dots representing global earthquakes.
*Of course, all themes in a view must share the same geographical coordinate system if they are to be properly displayed. Latitude and longitude are best for global maps, but other coordinates are frequently more appropriate for local or regional maps. UTM (universal transverse Mercator) uses meters or kilometers north and east of reference parallel and meridian respectively. Ohio uses a state plain system similar to UTM except using feet and different origin and axes. There are over 100 coordinate systems in use - many shapefiles in my computer will not work on this view.
Before doing anything fancy with the earthquake data, note that its extension is .txt, not .shp. In order to use the power of ArcView to work with earthquake data, a shapefile must be generated from this event theme.
Select the earthquakes theme, then "Convert to shapefile" (Theme menu). Navigate to your flash drive folder and save as (some descriptive name). Add the new shapefile theme to your view, and delete the .txt theme.
You can Query a theme by generating logical statements in the dialog window opened by hitting the Query button (the hammer, top row center of toolbar - no, this is NOT Tom DeLay) or by geographical associations. Because we are running out of time, we will do 2 simple spatial queries.
Query by graphic: Activate the earthquake theme. Use the polygon drawing tool to surround earthquakes around the Indonesian island of Java (east of Sumatra, the site of the deadly December 26, 2004 great earthquake). Then hit the "Select by graphic" button (which should appear to the left of the "Clear selected items" button, top row of toolbar). Dots representing earthquakes inside the polygon should turn yellow, indicating to you that they are selected. Now under the Theme menu, select "Convert to Shapefile" and save the new shapefile under a new name on your flash drive. Add this theme to your view and turn on this theme, after turning off the global earthquakes theme.
Query by theme: Activate the nations theme. Select the country of Perú. Now activate the global earthquakes theme. Under the Theme menu, select "Select By Theme" and have ArcView select all records from the active theme that are within 100 km of the selected item(s) of the nations theme. Now under the Theme menu, select "Convert to Shapefile" and save the new shapefile under a new name on your flash drive. Add this theme to your view and turn on this theme, after turning off the global earthquakes theme.
*Note that the distance units for 'distance' are the same as distance units for the view (reset using View - Properties if necessary).
(4) Classify each subset of earthquakes by depth (graduated color). Zoom to a view appropriate for seeing just the Java earthquakes. Export a layouts showing results as a .jpg image, with an appropriate title and your name. Attach this image to email addrssed to me. (5) Do the same for the earthquakes associated with Perú.