Part 2—Explore Data with a GIS
Step 1 Launch My World and Open the Seismic Wave Project File
- Launch My World GIS by double-clicking its icon on your desktop or by clicking its icon in the dock (Mac) or Launch Bar (PC).
- Choose File > Open Project and navigate to the file, Seismic Wave.m3vz. Select it and then click Open.
When the project opens, a world map displays. It shows Elevation and Bathymetry with outlines of Countries overlaid on top. Other layers in the project, but not visible on the map include:
- Plate Boundary types
- Earthquakes-Big 6.0-9.0
- Earthquakes-Medium 4.0-5.9
- Tectonic Plate Names
- Seismic S-wave Velocity at 28 km
- Seismic S-wave Velocity at 100 km
Step 2 Practice Moving around on the Map
- Select the Zoom In tool. Your cursor will now look like a magnifying glass with a plus sign in it.
- Click once on North America with the Zoom In tool.
- Click once on the Zoom to All tool
to take the map all the way back out to a full view.
NOTE: This is a nice trick if you get lost and just want to start over again.
- Continue clicking on the map with the Zoom In tool. The tool automatically centers the zoom level on the area where you click. How far can you zoom in?
- Click the Zoom Out tool several times. Keep clicking. How far can you zoom out?
- When you are done exploring zooming, click the Zoom to All tool.
- Click and drag out a rectangle across the contiguous U.S. States with the Zoom In tool. Notice how this allows for more precise zooming.
- Click the Zoom to All tool to return to the full map view.
- Two other buttons help you navigate on screen. They are the Zoom to Previous Extents and Zoom to Next Extents buttons. Try zooming in and then experimenting with these buttons. The Zoom to Previous Extents button lets you go back to a previous level of focus. Both of these buttons give you unlimited zooms back and forth between levels.
- When you are zoomed in, you can use the Move Map tool to adjust your view. Click and hold the Move Map tool and drag your mouse to center your map on another place.
- When you are done exploring zooming, zoom to the full extent.
As you zoom closer and closer on this image, you eventually see "pixels", or squares, of image data. However, most GIS data are vector-based, allowing you to continue to zoom in nearly infinitely.
Step 3 Add the Tectonic Plate Names and Explore Active Layers
Explore Active LayersTo the left of the map view is a listing of Layers, called the Layer List. In the Layer List, notice the checkbox to the right of the name of a layer. Click once in this box to turn a layer on and make it visible. Notice that when a layer is on, there is an eye in the checkbox.
- Turn on Tectonic Plate Names by clicking in the box next to its name. Layers that are on have an Eye in the checkbox.
- Notice that as you turn on a layer there is a legend for that Layer. To turn a legend on and off, click on the L symbol next to the words "Category List".
- Click anywhere in the box next to the name of a layer. The box will turn white and have a yellow highlight. This indicates that this layer is the Active layer. In the image below, Tectonic Plate Names layer is the active layer and the Legend for the Tectonic Plate Names is on.
- Open the Plate Tectonics layer's Table by selecting Layer > Show Layer Table... or clicking the Show Table of the Active Layer
button. In addition to appearing as a map layer in the map view, every layer in a GIS also has an associated table in which you can examine the data in a tabular format.
- How many records (plates) are in the table?
- Close the table when finished.
- Select the Get Information tool and click on some of the Tectonic Plates in the map view. The Information for Layer dialog box displays the information contained in the table for each plate you click. Close the Information for Layer window when you are finished exploring.
- Make Countries the active layer, turn on the Legend and use it to find Japan.
When you click on the name of a layer, it is highlighted and becomes active, which tells My World GIS to pay attention to it. Understanding the difference between a layer that is turned on and one that is active can save you time and help prevent frustration. A layer may be on or off as well as active or not. Layers that are on have a checked box while layers that are active are highlighted white with a yellow border. More than one layer can be on but only one layer can be active.
- Make sure the Highlight Mode is set to Color Selected (Yellow). Click once on the name Japan in the Legend for the Countries. Japan will be selected and highlighted on the map.
- Click the Zoom to Selection button to zoom to the extent of the selection, Japan.
- Once you have zoomed in to Japan turn off the highlighting by clicking the All (highlighting off) radio button. (It is located in the Layer List under the layer name.)
- Turn off (uncheck) the Elevation & Bathymetry layer.
Explore Moving Layers in the Layer List
- Turn on the Earthquakes-Big 6.0 -9.0 and Plate Boundary types layers.
- In the Layer List, select the Earthquakes-Big 6.0 -9.0 layer by clicking and holding its name. Drag the Earthquakes-Big 6.0 -9.0 layer up the list and place it above the Plate Boundary types layer. Each layer in a GIS builds the map. The data that make up the layers are shown as either points, lines, or polygons. These layers come from shapefiles, a standard GIS data format. (It is also possible to add images to a GIS as is shown here.) The layers are drawn from the bottom to the top as they appear in the Layer List. If not positioned properly, some layers may cover up others. In general, images and polygons should be placed at the bottom, while lines and points should be arranged near the top.
- Practice turning other layers on and off, and moving them up and down in the layer list.
- When you are finished exploring, turn off (uncheck) Earthquakes-Big 6.0 -9.0 and the Elevation and Bathymetry layers.