Materials
- Figs. 7.41–7.44
- World map, globe, or atlas
- Strip of paper
- Colored pencils
- Centimeter ruler
Procedure
A. Develop a contour map.
- Fig. 7.41 is a nautical chart of the Maug Islands in the western Pacific ocean basin.
- Using the latitude and longitude information given on the chart, locate this island group on a map of the world. Write down the location of the Maug Islands.
- The Maug Islands are three volcanic islands. Describe each island, including its size and elevation above sea level.
- On Fig. 7.41, locate the deepest sounding on the chart. Draw a box around the number.
- Using a light color, circle all depths 30 m or less. Choose a new color and circle all depths between 31 and 60 meters. Repeat this for 30-meter intervals.
- On Fig. 7.41, draw the contour lines for each interval of 30 meters (see Fig. 7.42).
- The 30 m contour line will encircle all of the depths less than 30 m.
- Remember that contour lines follow a single depth; lines should only go directly through depth readings that are the same as the labeled line.
- Soundings that are not the same as the labeled line will be intermediary between the 30-meter contour lines.
- Your contour lines should never intersect one another; they should continue completely around the island group (chart all of the islands as one group).

- Lightly shade the intervals between the contour levels using the shades you selected for each depth. Make a depth color key on the side of the chart.
- Suppose you were on a sailing ship that draws (extends below the waterline) 4 m. You want to sail your ship safely into the protected waters in the center of the Maug Island group and drop anchor.
- Study the chart to learn about each channel that leads from the open ocean into the protected central water. Describe each channel in terms of depth and hazards to navigation.
- Decide how you would sail from open ocean into the center of the island group. With the ruler, mark a straight line on the map showing the course you would choose.
B. Develop a depth profile.
Your contour map shows a “bird’s eye view” of the Maug Islands. To get a “fish’s eye view,” a depth profile will be needed.
- Extend the line you drew in Procedure 6 to mark your course into the center of the island group so that it becomes a transect line cutting across the entire chart, including a portion of any of the islands.
- Lay the edge of a strip of paper alongside the line you drew to mark the course you took to the center of the island group (Fig. 7.43 A). This line is your transect, a line that you follow to record data in specific locations.
- Mark the strip of paper at each point where the edge of the paper strip touches a contour line and record the depth or elevation alongside the mark (Fig. 7.43 A).

- Make your own grid like that in Fig. 7.44. Label each axis.
- The horizontal axis represents the distance across the transect line.
- Note that the chart in Fig. 7.44 gives a scale for distance. The vertical axis represents the depths below sea level and the elevations above sea level in meters.
- Do not forget that sea level is 0, so some of your points will be above and some will be below 0.

- Place the paper “transect” along the bottom of the grid as shown in in Fig. 7.43 B, and transcribe the depth information along the base of the graph.
- Plot each depth and elevation marked on the paper strip.
- Hold the strip along the horizontal axis of the grid and make a dot corresponding to each contour line marked.
- Read the depth or elevation marked on the strip, beginning with the first mark on the left.
- Move your pencil straight up from the mark on the bottom to the appropriate level on the grid and make another mark at the corresponding depth or elevation.
- Use a ruler to help you stay directly above the mark on the horizontal axis.
- Draw the profile by connecting all the depth and elevation marks. This will show you the side view of the islands.