Week 7: Investigating Global Earthquake Activity
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Download Geographic Data About Earthquakes
Explore a Table of Data
Launch ArcGIS and Open the Earthquakes Project
Review How Longitude and Latitude Appear on the Map
Put Tabular Data on the Map
Classify and Symbolize the 2009 Earthquake Data
- Classify the 2009 earthquakes by magnitude
- Classify the 2009 earthquakes by depth
- Explore other classification and symbolization options
- Convert XY Data to Shapefile
Choose Another Tabular Dataset to Add to Your Map
Explore More If You Have Time
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Intro to Mapping Tabular Data in ArcGIS
In the first few weeks of this module you have used GIS to explore many types of shapefiles. Whether looking at city populations, river drainage areas or invasive species counts per county, we have provided you this data. This week we will start to add point data from longitude and latitude documents. GIS can easily draw this data as a point feature once imported into a GIS from a table of data. With this technique in your skill "toolkit" you can easily add data from thousands of sources, or even create your own data with a GPS unit.
Download Geographic Data About Earthquakes
- Right-click on the PC to download the zipped file below.
EarthquakeAM.zip (Zip Archive 14.6MB Mar28 10) - Unzip the file. A folder called EarthquakesAM will be created.
- Move the entire EarthquakeAM folder to inside the folder of Week7. The navigation path should be: (Path: c:/eyesinthesky2/week7/EarthquakeAM)
Explore a Table of Data
Think about the last time you collected a set of data. You probably set up a data table with headers indicating the data you wanted to collect, including the units that would be collected. The rows of that table were set up to hold the data for each individual record or event that you planned to collect. As you made observations, you filled in the data table with whatever observations you made of each event. The table was probably organized sequentially, with the first row being the earliest event and so on.
After the experiment was concluded you used this data table to begin the analysis of your results. Maybe you graphed the data or looked for patterns or clusters of data. You may have used a spreadsheet program to analyze this data, especially if you were doing a more complex analysis.
Examine the excerpt of a table of numbers and other information pictured below. This table shows earthquakes that occurred in 2009. The data table is similar to other attribute tables that you have been working with so far in this course.
Thought Question: What are the advantages and disadvantages of working with data in a tabular format?
What is absent in exclusively tabular data is the opportunity to easily inquire about spatial relationships. Fortunately, many Earth and environmental science datasets available today include some sort of geospatial reference. When the spatial data, or Longitude/Latitude data, (also called X, Y data), are included alongside other information, it is possible to place that data onto a map and see it in a richer, more complete environment.
The classic example of a map illuminating the answer to a complex problem was John Snow's pump handle and cholera incidence map. Can you think of other patterns that are more easily understood with a map than a list or table of data?
GIS software can convert any table, or delimited list of information, into a GIS map if coordinate data (Longitude and Latitude) are included with it. This week you will learn how to import and save these kinds of data into a native GIS format.
Launch ArcGIS and Open the Earthquakes Project
- Launch ArcGIS ArcMap by double-clicking its icon on your desktop or Launch Bar.
- Choose File > Open, navigate to c:/eyesinthesky2/week7/EarthquakeAM, select the EarthquakeAM.mxd file, and click Open.
- A global map opens with the Continents, US States, and Lines of Longitude and Latitude on the map.
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Review How Longitude and Latitude Appear on the Map
Move the cursor across the map to remind yourself how the X and Y coordinates relate to Longitude and Latitude. Start at the far left side of the map and move your cursor horizontally to the right all the way across the map. The X and Y coordinates are shown in the lower left corner of the map. Notice how the X coordinates show changes in longitude. Move your cursor vertically from the bottom to the top of the map. Notice how the Y coordinates show changes in latitude.
Map showing XY (longitude, latitude) coordinates. top of page
Put Tabular Data on the Map
Add Earthquake data from 2009
To map the 2009 earthquake events using Longitude and Latitude coordinate, select Tools > Add XY Data. The Add XY Data window opens. Navigate to the file named 2009EQ.csv. (c:/eyesinthesky2/week7/EarthquakeAM/csv_files). Select Longitude for the X Field and Latitude for the Y Field. The options in the Add XY Data window are as follows:
- Select X field: Longitude
- Select Y field: Latitude
- Click OK.
- The 2009EQ.csv file will add to your Table of Contents. Accept the symbolization that is automatically selected by the program. The colors are randomly selected and may differ from your own symbol colors.
Show me how
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The 2009 Earthquakes will now be displayed on the map.
Note: If you miss-assigned the X and Y fields, the data will look strange, perhaps in a straight line, or as a single dot or in the wrong part of the world. Just right click and delete the new layer then repeat the steps above. The most common problem is switching the Latitude and Longitude (i.e.Latitude as X and Longitude as your Y fields).
You can see with your mouse that the X coordinate changes moving from one longitude line to another on the map and the Y coordinate changes as you move between lines of latitude.
At the end of this lesson you will export a corresponding shapefile to the XY layer in the Table of Contents. After you create a shapefile of your XY data, the computer will ask if you want to add it to the project. Alternatively you can click the Add Data button and look for the shapefile of the same name as the original table in the Earthquakes CSV file folder
For the 2009 Earthquake data, you will find a file called 2009EQ.shp, that has a .shp extension.
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Classify and Symbolize the 2009 Earthquake Data
Once the earthquake data is on the map, it is possible to Classify and Symbolize it.
Classify the 2009 Earthquakes by Magnitude
To open the Properties window for the 2009 earthquakes layer, right-click the 2009EQ Event layer in the Table of Contents. Choose Properties from the menu. Then select the following options:
- Draw features using: Quantities > Graduated Symbols
- Field Magnitude
- Classes 5
- Style Circle1
- Classified by Equal Interval
- Size Start 2 and End 12
- Click OK
