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.

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.”

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.

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

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.

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.

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