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 City of San Francisco appear closer to its actual size and shape on Earth.
Open the data frame properties. If you will recall from a previous activity, in the Table of Contents, the word Layers appears above the map layers. If you will remember from previous tutorials, 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 “San Francisco Basemap.”
Select the Coordinate System tab. Scroll down until you see the Projected Coordinate Systems folder. Expand the folder, then, expand the UTM folder. Locate the folder that says NAD 1983 and open it. Select NAD 1983 UTM Zone 10N from the list and 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 this session. Click Yes to close the warning.
At such a large scale, you may not notice a dramatic change to the shape of the city. Nevertheless, optimizing the appearance of the spatial reference system displayed on the data frame is an excellent habit to develop for cartographic design. Take a moment to save your map document before moving on to the next step.