# Learning About Projections Using ArcGIS

## Exploring Map Projections

In this chapter, you learned that Earth is spherical. However, maps still managed to represent Earth using a flat plane. A flat representation is made possible by using map projections. A map projection is a geometric transformation of the round Earth onto a flat plane using mathematical equations. The process of transforming a spherical object onto a flat plane distorts area, shape, distance, direction, and continuity. These are known as the five preserved properties because some map projections can maintain one or more of these characteristics with a high degree of accuracy. However, no map projection can retain all five of these qualities at the same time.

In ArcMap, the data frame window displays the map using project-on-the-fly. Even though the layers in the Table of Contents might use different projections and coordinate systems internally, ArcMap tries to line them up on the screen using the coordinate system defined in the data frame properties. What this means is that you can change the projection in the data frame to alter the appearance of the map onscreen without modifying the original data files.

### Cylindrical Projections

Cylindrical projections transform the globe onto a flat plane using a cylinder as the developable surface. In this step, you will use ArcMap to explore one of the most commonly used cylindrical projections, the Mercator.

Open the properties for the world map data frame. Navigate to the Coordinate System tab. Expand the Projected Coordinate Systems folder.

Scroll down until you see the World folder. Expand the World folder and select Mercator (world). When you are ready, click OK. Click Yes, when the warning appears. On the Tools toolbar, click the Full Extent button, which looks like a globe.

Take a moment to review the chapter text regarding the Mercator projection. When done, continue to the next step.

By default, the Mercator projection centers on 0 degrees longitude. However, in ArcMap, you can customize map projections to a certain extent. What you are allowed to do varies by map projection. For the Mercator projection, it is possible to center the map on any longitude you wish. In this step, you will align the map on the opposite side of the globe, 180 degrees longitude.

Open the properties for the data frame and navigate to the coordinate system tab. Double-click on the Mercator (world) projection. When the Projected Coordinate System Properties window appears, change the name to “World Mercator 180.” In the Value field for the central meridian, enter 180. When done, click OK. Then, click OK again to apply the changes to the data frame. Click Yes to close the warning.

You should immediately notice that the map rotates so that the Pacific Ocean is in the center. You have just created your first customized projection.

Another commonly used cylindrical projection is the Transverse Mercator. Open the properties for the world map data frame. Navigate to the Coordinate System tab. Expand the Projected Coordinate Systems folder. Scroll down until you see the UTM folder. Expand the UTM folder and scroll down until you see the NAD 1983 folder. Expand the folder and choose NAD 1983 UTM Zone 10N.

When you are ready, click OK. Click Yes, when the warning appears. On the Tools toolbar, click the Full Extent button.

Take a moment to review the chapter text regarding the Transverse Mercator projection. When done, continue to the next step.

By default, Zone 10 is centered on Northern California. Normally, when you want to use the Transverse Mercator for a different region, you would choose the appropriate zone. However, it is possible to center the Transverse Mercator to a location manually. Using the same methods as before, create a customized Transverse Mercator projection. Change the central meridian to 57. Name the customized projection “Transverse Mercator 57.”

### Conical Projections

Conical projections transform the globe onto a flat plane using a cone as the developable surface. In this step, you will use ArcMap to explore one of the most commonly used conical projections, Lambert Conformal Conic.

Open the properties for the world map data frame. Navigate to the Coordinate System tab. Expand the Projected Coordinate Systems folder. Scroll down until you see the Continental folder. Expand the Continental folder, then expand the North America folder. Choose North America Lambert Conformal Conic. When you are ready, click OK. Click Yes, when the warning appears. On the Tools toolbar, click the Full Extent button, which looks like a globe.

Take a moment to review the chapter text regarding the Lambert Conformal Conic projection. When done, continue to the next step.

This version of the Lambert Conformal Conic projection is centered on North America. Using the same methods as before, create a customized Lambert Conformal Conic projection centered Japan. Change the central meridian to 140. Name the customized projection “Japan Lambert Conformal Conic 140.”

### Planar Projections

Planar projections transform the globe onto a flat plane using a plane as the developable surface. In this step, you will use ArcMap to explore one of the most commonly used planar projections, the Stereographic.

Open the properties for the world map data frame. Navigate to the Coordinate System tab. Expand the Projected Coordinate Systems folder. Scroll down until you see the Polar folder. Expand the Polar folder. Choose, North Pole Stereographic. When you are ready, click OK. Click Yes, when the warning appears. On the Tools toolbar, click the Full Extent button.

Take a moment to review the chapter text regarding the Stereographic projection. When done, continue to the next step.

This projection is obviously centered on the North Pole. If you wanted a map centered on the South Pole, you could choose the South Pole Stereographic. However, customizing the North Pole Stereographic provides an opportunity to change a different projection parameter, the Latitude of Origin.

Using the same steps as before, open the Projected Coordinate System Properties for the North Pole Stereographic projection. Change the Latitude of Origin from 90 to -90. This step will flip the map so that it is centered on the south pole. Name the customized projection “North Pole Stereographic Flipped.”

When you are ready, click OK. Click Yes, when the warning appears. On the Tools toolbar, click the Full Extent button.

Another commonly used planar projection is the Azimuthal Equidistant. Open the properties for the world map data frame. Navigate to the Coordinate System tab. Expand the Projected Coordinate Systems folder. Scroll down until you see the Polar folder. Expand the Polar folder. Choose, South Pole Azimuthal Equidistant. When you are ready, click OK. Click Yes, when the warning appears. On the Tools toolbar, click the Full Extent button.

Though it is a planar projection and also centered on the south pole, it appears entirely different than the stereographic projection from the previous step.

Take a moment to review the chapter text regarding the Azimuthal Equidistant projection. When done, continue to the next step.

### Compromise Distortion Projections

Compromise distortion projections do not try to preserve any of the map projection properties. Instead, they are designed to appear aesthetically pleasing, balancing shape and area. Using what you have learned, change the data frame projection to Robinson (world). It is located in the World folder under Projected Coordinate Systems. Change the Robinson projection so that it is centered on Humboldt County (central meridian -124). Name the customized projection “Robinson Humboldt.”

Take a moment to review the chapter text regarding compromise distortion projections. When done, continue to the next step.