Week 7: Investigating Global Earthquake Activity

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Intro to Mapping Tabular Data in My World

 

In the first few weeks of Module 2, you used GIS to explore many types of databases and their associated shapefiles. Features that can be drawn as points can 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.

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Download Geographic Data About Earthquakes

  • Right-click (Win) or control-click (Mac) the link below to download the zipped file. 
    EarthquakeMW.zip (Zip Archive PRIVATE FILE 19.8MB Jun13 10)
  • Unzip the file. A folder called EarthquakesMW will be created.
  • Move the entire EarthquakeMW folder into the Data folder inside the My World folder. (Path: Applications/My World/data/ EarthquakeMW.)

 

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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 bring 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.

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Launch My World and Open the Earthquakes Project

 

My World Icon

  • Launch My World by double-clicking its icon on your desktop or by clicking its icon in the Dock (Mac) or Launch Bar (Win).
  • Choose File > Open Project, navigate to Applications/My World /data/ EarthquakeMW, choose the E_QuakesMW.m3vz file, and click Open.
  • A base map opens, showing Continents, U.S. States,and Lines of Longitude and Latitude.

 



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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.

lat long EQ Map showing XY (longitude, latitude) coordinates.

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Put Tabular Data on the Map

 

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Add earthquake data from 2009

 

To map the 2009 earthquake events using Longitude and Latitude coordinates, choose File > Import Layer from File. add layer from file Single click to select the file, 2009EQ.csv and then click Open 2009EQ.csv. (Path: Applications/My World /data/EarthquakesMW/csv_files).

  • The Import Text Data dialog window the fields for your data are set to display Latitude and Longitude properly. It is set up correctly, so click OK. My World GIS imports the tabular data, places it on the map and saves a copy in the My World "data" folder on your computer.
  • The new data layer should now be visible on the map and in the Layer List. Drag it to the map and make it the Active layer and click the Zoom to Active Layer zoom to active layer button in the toolbar.

  • Symbolize the new layer to display medium sized blue circles.

 

The 2009 Earthquakes will now be displayed on the map. (Be patient. importing a CSV file especially one with many features may take time, especially on slower computers.)


  • Save the CSV file as an "ESRI shapefile". Choose Layer > Save Layer As ... and save the newly imported and symbolized layer to the EarthquakesMW folder.

Note: If you enter the Latitude and Longitude 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.

The good news is you only have to go through this import process once. When My World 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 Layer from File button and look for the shapefile of the same name as the original table in the EarthquakesMW folder. For the 2009 Earthquake data, you will find a file called 2009EQ.shp, that has a .shp extension.

 
Movie Icon

 

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Classify and Symbolize the 2009 Earthquake Data

 

Once the earthquakes are displayed on the map, you can Classify and Symbolize them.

 

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Classify the 2009 earthquakes by magnitude

 

To open the Edit Appearance window for the 2009 earthquakes layer, double click the 2009EQ label in the Layer List. The Edit Appearance window will open. Select the following options:

  • Choose Color by: Magnitude
  • Color Count 5
  • Shape Circle
  • Classify by Equal Interval
  • Colorscheme Red
  • Size 20%
  • Click Apply and click Close