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

Changing the Map Projection of the Data Frame

The Earth is spherical, yet maps still managed to represent the Earth using a flat plane. Map projections make this possible. A map projection is the geometric transformation of the round earth onto a flat plane using mathematical equations. In a later chapter, you will learn more about map projections. What you need to understand now is that there are many different map projections. The one you choose will change the shape and appearance of features on the map. In this step, you will change the map projection for the data frame to make the State of California appear closer to its actual size and shape on Earth. In ArcMap, zoom out until you see the entire continental United States. This view will help you to understand the difference in appearance between projections.

An image of ArcMap zoomed out to the United States
The United States has a slightly curved shape. When you see it represented with a flat top, you know it is not in the optimal projection. Click to view a larger sized image.

Open the data frame properties. If you will recall from a previous activity, in the Table of Contents, the word Layers appears above the four map layers. Esri made a lousy choice when naming this element in the Table of Contents. The name consistently leads to confusion. This item on the Table of Contents is not a layer. It represents the data frame. Access the properties for the data frame by right-clicking on the word Layers in the Table of Contents. Select, Properties from the contextual menu.

When the Data Frame Properties window opens, click the General tab. Change the name of the data frame to something more descriptive, such as “California Earthquakes.”

An image of the data frame properties window for earthquake map
Changing the name of the data frame helps to add clarity to the Table of Contents. Click to view a larger sized image.

Select the Coordinate System tab. Scroll down until you see the Projected Coordinate Systems folder. Expand the folder, then, expand the Continental subfolder. Locate the North America subfolder.

An image of the North American subfolder
Be sure you are selecting the North America folder from the Projected Coordinate Systems folder.

Within the North America folder, select North America Lambert Conformal Conic. Then, click OK.

An image of the Lambert projection selected
The North American Lambert Conformal Conic projection is optimized for the North American Continent. Click to view a larger sized image.

You may get a warning. ArcMap is telling you that the data frame coordinate system does not match some of the layers in the Table of Contents. Since we are only using it for display purposes, this is fine. Check the box that says, Don’t warn me again in this session, and click Yes to close the warning.

An image of the Data frame geographic coordinate system warning
Click to view a larger sized image.

You should notice an immediate change to the size and shape of the United States. The Lambert Conformal Conic project works well to make the U.S. appear closer to the way it does on Earth. The size and shape of the individual states are also closer to reality.

An image of the United States in Lambert Conformal Conic
The North American Lambert Conformal Conic projection displays the correct shape of the United States. Click to view a larger sized image.

Zoom back into your earthquake layer and save your map document before moving on to the next step.