# 8 Measure the area of erosion

** Step 1**

To calculate the area of coastline that has eroded, work with the image that shows the difference between the 1985 and 2005 Landsat satellite images. From the toolbar click on the Polygon selections tool.

Step 2

Select an area on the image that shows change. Click around the area. Close the polygon by clicking on the starting point, which appears as a square until clicked.

** Step 3**

From the menu select Analyze → Measure.

Results will show in a new window. Expand the window to see the area measurement. The area will be in square meters.

- Roll-over for Answer:
- In this example, 1,152,000 square meters of the coast are shown to have eroded from

1985 to 2005. Results will differ based on the shape of the polygon that is drawn.

**Making Sense of the Number**

The surface area lost measures about half a square mile, an area 1 mile x .5 mile. This would be 210 football fields.

1,152,000 square meters / 5,390 square meters (the area of a football field) = 210.

The surface area of other parts of the coast can also be measured. A scientist would take careful measurements of the whole area to get the best measurement.

*Step 4 describes how to calculate the volume of this area. Volume describes a three dimensional measurement, quantifying how much soil a hand or a container could hold, for example.*