Urbanization

Purpose

“Gilbert has experienced a rapid transition from a historically agriculture-based community to an urban center and suburb in the Phoenix Metropolitan Area. In the last decade and a half, Gilbert has grown at a pace unparalleled by most communities in the United States, increasing in population from 5,717 in 1980 to over 127,000 in January 2002.” – City of Gilbert website (http://www.ci.gilbert.az.us)

Tools

One of the tools on the RangeView Web site is the Arizona Map Server. It allows users to view a satellite image with selected map layers displayed over it. Users can also zoom in and out, pan side to side, and measure distances on the image.

In addition to the AVHRR images used in the animations, the Map Server features two Landsat TM images from 1993 and 1999, which each have a resolution of 30 meters.

Exercise: Using the Map Server

Zoom In and Out

1. Open the Map Server Tool. It may take a minute for the greenness image of Arizona to load in the map viewer.

2. Locate a set of tools at the top of the browser window, above the Arizona image. Hold the cursor over an icon without clicking to display a tooltip with the name of the tool.
   
   

   	Zoom In: Click once to zoom farther in on the image, or hold down the mouse button and drag to draw a box around the desired viewing area. The map server will automatically reload the image.
   	Zoom Out: Click anywhere in the image to zoom out.
   	Pan: Hold down the mouse button and drag the image up or down, or to the right or left, to re-center the image.
   	Zoom to Full Extent: Click on tool icon to zoom out to all of Arizona.

Choose Display Layers

On the right side of the Map Server window, you will find a list of layers which can be displayed in the map window. In the list, you will find map data for several ranches and National forests that are participating in RangeView.

Below the data set for the V-Bar-V Ranch are the sets of satellite imagery available for display in the window.

1. Click on the layer stack next to “2003 AVHRR Greenness Images.” This will expand a list of all layers in this category.
2. Uncheck the box next to “Sep 16 2003 greenness” to turn off the current greenness image of Arizona.
3. Click on the layer stack called “Landsat TM/ETM+ Satellite Images.”
4. Check the box next to “1993 Landsat TM False Color Composite” to turn on the 1993 Landsat image.
5. Click "Refresh Map."

Map reference layers, which are displayed over the satellite images, provide reference points necessary to find specific areas on the map.

1. Select the checkboxes next to Towns, Roads (Medium), and Counties at the bottom of the Layers list.
2. Click "Refresh Map" to redraw the map with overlaid features.
3. The "active" layer is highlighted in blue.

Landsat TM/ETM+ imagery (30 m) is at a much higher resolution than AVHRR imagery (1 km). This means you can zoom in further and see more detail.

The image is displayed as a “False Color Composite,” which is much like a color infrared photograph. The colors in the image do not appear as you would see them with your eye. Of particular interest is the fact that the vegetation does not appear green; it appears red.

Notice that the Mogollon Rim appears bright red in comparison to the rest of the image. This is because it is a ponderosa pine forest and, hence, a highly vegetated area.

1. Can you see any other areas that are highly vegetated, such as areas along a river?

Zooming in on Gilbert

Use the Zoom In tool to zoom in on the eastern portion of Maricopa county, the section north of Pinal county. The window will automatically refresh. You will see the Phoenix metropolitan area. Gilbert is southeast of Phoenix. Use the Zoom In tool again to draw a box around Gilbert, Chandler, and Higley. Wait for the map to refresh.

Recall from the quote at the beginning of the exercise that Gilbert is a “historically agriculture-based community” and that in this image vegetation is displayed as red.

2. What do you think the bright red squares in the image are?

3. What kind and how much change do you expect to see between the 1993 and 1999 image?

Change from 1993 to 1999

1. In the layer list, click the layer stack next to “Landsat TM/ETM+ Satellite Imagery” to expand the list if it is not already expanded.

2. Uncheck the box next to “1993 Landsat TM False Color Composite” and check the box next to “1999 Landsat ETM+ False Color Composite.”

3. Press the “Refresh Map ” button.

4. Use the “Back” and “Forward” buttons in your Internet browser to alternate between the 1993 and 1999 images.

4. Where did you see the most significant change?

5. Notice that there is still red in this area. It is not as bright as the agricultural areas, but appears textured. Knowing that Gilbert has become more urban and residential, what sort of vegetation do you think the satellite is detecting?

In Application 3, we will learn about the way that satellites take these images. Consider what information would be useful in interpreting these images further.

Discussion Questions

6. What are the advantages and disadvantages of a tool like the Map Server compared with the Dynamic Animations?

7. Besides detecting change, what are other uses for the data on the Map Server?

8. How well were you able to interpret the Landsat TM images?