Mapping Earthquakes in Northern California

Table of Contents

  1. Mapping Earthquakes in Northern California
  2. Setting Up Your Workspace
  3. Downloading Data from Natural Earth
  4. Download Data from the Northern California Earthquake Data Center (NCEDC)
  5. Skill Drill: Download Data from the United States Census Bureau
  6. Adding California as a Basemap Layer
  7. Skill Drill: Adding the Humboldt County Boundary as a Basemap Layer
  8. Adding XY Data
  9. Changing the Map Projection of the Data Frame
  10. Representing Earthquake Magnitude Using Graduated Symbols
  11. Changing the Map Size and Position
  12. Creating an Inset Map
  13. Inserting A Map Title
  14. Inserting a Map Legend
  15. Inserting a North Arrow, Scale Bar, and Acknowledgments
  16. Exporting your map as a PDF file

Adding California as a Basemap Layer

In geospatial science, a basemap refers to a collection of data layers that are used to create a background for the map. The purpose of a basemap is to provide context for the primary data, both spatially and thematically. Typical basemap layers include roads, administrative boundaries, and aerial imagery. In this activity, the state and county boundaries serve as the basemap layers.

Locate ArcMap on your computer and launch the software. If you are using Microsoft Windows 10, click the windows button and type ArcMap to find the desktop application.  Launch the ArcMap software.

An image of the Windows 10 Start Menu
The actual version of ArcMap may vary over time. Click to view a larger sized image.

When you first launch ArcMap, a window appears that gives you the option to either open a blank map or to open any of your recent map documents. Choose to open a blank map document.

An image of the ArcMap getting started window
The ArcMap Getting Started window provides several options on startup.

The ArcMap user interface has three main windows that you use on a regular basis, the Table of Contents, the data frame, and the Catalog Window. The Table of Contents displays a list of data frames and map layers loaded into the map documents. The data frame, sometimes spelled dataframe, represents the layers in the form of a map and defines the map extent. The Catalog Window displays a hierarchical view of folder connections and data in the form of a Catalog Tree.

An image of the blank map document
From left to right, the three main windows are the Table of Contents, the data frame, and the Catalog Window. Click to view a larger sized image.

The icon for the catalog window looks like a yellow file cabinet. If your catalog window is missing, you can find the icon on the toolbar across the top. Click to open it back up.

An image of the Catalog Window Icon
Click the yellow file folder icon if your Catalog Window is missing.

In this step, you will start by working with the Catalog Window. The catalog window is where you manage your geospatial data in ArcMap. Start by clicking on the Connect to Folder button. Navigate to your workspace folder, Earthquake_map, on your local hard drive.

An image of the connect to folder button in the Catalog Tree
You connect to a folder so that the contents will appear in the Catalog Window.

In this step, it is essential that you select your primary workspace folder, Earthquake_map, to add it to the Catalog Window. When ready, click OK.

An image of the connect to folder window for GSP 101 earthquake map
Connect to Folder will add the folder to the Catalog Window.

Once you add your workspace folder to the Catalog Window, expand the folder by clicking on the plus sign. You should see your three subfolders inside. Expand the original folder to view the contents. This display of folders and files within the Catalog Window is sometimes called the Catalog Tree.

In a previous activity, you learned how to add data to ArcMap. Add the states and provinces layer to the map.

An image of the states and provinces layer
Natural Earth provides data for the entire globe. Click to view the image in a larger size.

In a previous activity, you learned how to use various zoom tools. In ArcMap, zoom to the State of California and surrounding areas. Try to set your map so that California takes up most of the space.

An image of the map zoomed to California
The map extent displays the State of California and surrounding areas. Click to view a larger sized image.

Because California is the primary geographic extent for your earthquake maps, you will want to be able to distinguish California from the other states. You will do this by creating a new shapefile with California as the only polygon feature.

In a previous activity, you learned how to directly select features on the map using the select features tool. Use the tool to select the State of California. On the Tools toolbar, click the Select Features tool. The icon looks like a white arrow over a blue and white square. Then click on California. When you have a feature selected in ArcMap, you have the option to export it as a new shapefile. With California selected, right-click on the states and provinces layer in the Table of Contents. Select, Data, then Export Data.

An image of export data option in the Table of Contents
You can access contextual menus by right-clicking. Click to view a larger sized image.

When the Export Data window opens, you will see some options. Next to Export, be sure it says Selected features. Next, click the yellow file folder icon and browse to your Working folder.

An image of the Export Data window for California
You have several options to choose from when exporting data.

Never accept the default output location in ArcMap. Always browse to the folder location you intend to use. This step will help prevent lost data.

Next to Save as type, choose Shapefile. Name the file “California” and click Save, then click OK. When ArcMap asks if you want to add the exported data as a map layer, click Yes.

An image of the Saving data window for California
When saving data, make sure you are in the correct folder. In this example, it is the Working folder.

The California layer gets added to the Table of Contents. On the map, California remains selected. Clear the selection by clicking on the Clear Selected Features button. Your map document now has two layers, one representing the State of California and one that currently displays the surrounding States and Mexico.

An image of the California added to the map
When you add new layers to ArcMap, the software randomly chooses colors. Click to view a larger sized image.