Week 7: Investigating Global Earthquake Activity
Introduction to Mapping Tabular Data in AEJEE
In the first few weeks of the module you used GIS to explore many types of databases and their associated shapefiles. Features that can be drawn as points can easily be imported into a GIS from a data table. Once you have this technique in your skill toolkit, you can easily add data from thousands of sources, or even collect your own data with a GPS unit to add as a map layer.
Download Geographic Data About Earthquakes
- Right-click (Win) or control-click (Mac) the link below to download the zipped file.
EarthquakeAE.zip (Zip Archive 14.5MB Mar26 10) - Unzip the file. A folder called EarthquakesAE will be created.
- Move the entire EarthquakeAE folder into the Data folder inside the AEJEE folder. (Path: ESRI/AEJEE/Data/EarthquakeAE.)
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 rows being the earliest events and so on.
After the experiment was concluded you used this data table to analyze your results. Maybe you graphed the data or looked for patterns or clusters in the data. You may have used a spreadsheet program to analyze this data, especially if you were doing a more complex analysis.
Examine the data table below. It contains both numerical and descriptive data. This table shows earthquakes that occurred around the world in 2009. The data table is similar to other attribute tables that you have worked with 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 context.
The classic example of a map illuminating the answer to a complex problem was John Snow's water pump 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 these kinds of data.
Launch AEJEE and Open the Earthquakes Project
- Launch AEJEE by double-clicking its icon on your desktop or by clicking its icon in the Dock (Mac) or Launch Bar (Win).
- Choose File > Open, navigate to ESRI/AEJEE/Data/EarthquakeAE, choose the E_QuakesAE.axl file, and click Open.
- A base map opens, showing Continents, US States,and Lines of Longitude and Latitude.
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. Put Tabular Data on the Map
Add earthquake data from 2009
To map the 2009 earthquake events using Longitude and Latitude coordinates, choose View > Add Event Theme. The Add Event Theme window opens. Click the Browse 
button to navigate to the file named 2009EQ.csv. (Path: ESRI/AEJEE/Data/EarthquakesAE/csv_files). Choose Longitude for the X Field and Latitude for the Y Field. Draw the events using symbols that are Blue Circles with a point size of 5. The options in the Add Event Theme window are as follows:
- Table: ESRI/AEJEE/Data/EarthquakesAE/csv_files/2009EQ.csv
- X field: Longitude
- Y field: Latitude
- Draw event using symbol with:
- Style: Circle
- Color: Blue
- Size: 5
- The Output Directory defaults to the current csv_files folder that you opened the earthquake file from. Accept this default.
- Click OK.
Show me how
Hide
The 2009 Earthquakes will now be displayed on the map. (Be patient. Adding an event theme — especially one with many features — may take time, especially on slower computers.
Note: If you enter the X and Y fields incorrectly, the data will either not project or will project incorrectly. Repeat the steps above.
The most common problem is choosing the wrong fields to use for Latitude and Longitude. Recall that X coordinates represent the vertical, or longitude, lines on the map and Y coordinates represent the horizontal, or latitude, lines.
The good news is you only have to go through this import process once. When AEJEE imports and projects a tabular dataset onto a map it automatically creates and saves a corresponding shapefile. The next time you want to see this dataset on your map as a layer, just click the Add Data button and look for the shapefile of the same name as the original table in the Earthquakes csv files folder. For the 2009 Earthquake data, you will find a file called 2009EQ.shp, that has a .shp extension.
Classify and Symbolize the 2009 Earthquake Data
Once the earthquakes are displayed on the map, you can Classify and Symbolize them.
Classify the 2009 earthquakes by magnitude
To open the Properties window for the 2009 earthquakes layer, right-click (Win) or control-click (Mac) the 2009EQ label in the Table of Contents. Choose Properties from the menu. Then select the following options:
- Draw features using: Graduated Symbols
- Field Magnitude
- Classes 5
- Style Circle
- Classified by Equal Interval
- Color Start White and End Red
- Size Start 2 and End 12
- Click Apply and Click OK
