Geol 301 Spring 2007Visualizing the Earth: Topography and Topographic Maps

Concepts and Terms:

Visualizing 3D in 2D Contour Interval Contour lines Gradient Index Contours Latitude and Longitude Profiles Relief Rule of “Vs” Scale Vertical exaggeration Finding Topographic Map and other visualization of the Earth

Part 1. Hands-on model topography map in 3DTogether we will build a 3-D model of a 2-D map of a 3-D surface. How is that for going full circle!

Before we begin examine the map. On it are several contour lines. Points on any particular contour line is the same elevation as any other points on that same line. Thus the spatial distribution of labeled contour lines can display the lay of the land – the different highs and lows in the landscape.

1. Describe the landscape (shape of the land) of this region just based on the map alone.

2. Let’s model this to see what the landscape looks like in 3D. Describe the landscape now with the 3D model.

3. We will put thicker spacers in our model. How did this change what you see in the model?

Part 2. Computer assisted visualization of 3D in 2D

Material adapted from: http://reynolds.asu.edu/

From this main link choose: Visualizing Topography from the side menu and then choose click to enter.

Background: Topographic Maps Module Student GuideIn this module, you will learn more about topographic maps – one method of showing thevarying elevations of an area using lines (contour lines) that represent a single elevation. You will be able to view movies showing three landforms: hill, valley, and cliff. For each landform you will first see its topographic map and then interact with movies showing each landform’s three-dimensional features.

The purpose of this module is to help you learn to visualize the three-dimensional surfaceof a landform from two-dimensional topographic maps. Observations of students readingtopographic maps have shown that students struggle with this interpretation exercise. Themovies that are included in this module helped those students to improve their map-reading, interpretation, and visualization skills.

Some of the movies included in this module are virtual reality (VR) movies and allowyou to click-and-drag the mouse inside the image to change features of the movies. Note it is important to wait to click and drag until after the Quicktime file is completely loaded. Above each movie, arrows will indicate the direction(s) you can move the mouse and text will indicate what changes will occur as you drag the mouse in each direction. Other movies are self-playing, and after a short pause on the screen, they will begin playing without you having to do anything. Once these movies reach the end, they will repeat from the beginning.

There are several different types of movies in this module.Tilt and rotate. In the VR version, you can click-and-drag the mouse to 1) rotate themovie 360° (by clicking and dragging side-to-side) and 2) tilt the landscape on itsside to view elevation differences (by clicking and dragging up and down).Shading. These movies allow you to watch shadows lengthen and shorten acrosssurface features and show you how shadows would change as the sun rises and sets.Flooding. These movies allow you to flood a given landscape and watch how waterfills a terrain.Profile-slicing. These movies allow you to cut into a landscape from front to back tosee how profiles (side views) of the landscape change and how topographic mapswould look if viewed from the side.

The research group that developed this module feels the best way for you to learnabout topographic maps is to play with the movies we’ve made for this module. For you to get the most out of this, you might have to look at each movie a few times. Before you start the module, make sure you have the worksheets handy! We included these to help you keep a record of your answers to questions, observations, and progress as you go through this module.

Instructions: Work through the Visualizing Topography module on the computer. Put your observations and answers in the appropriate spaces below.

1. By now you have a picture in your mind of what this landscape looks like. In the space provided below, write a description of this landscape so that someone who had not seen it before could imagine it in their mind.

Landscape Description:

2. By now you have a picture in your mind of what this landscape looks like. In the space provided below, write a description of this landscape so that someone who had not seen it before could imagine it in their mind.

Landscape Description:

3. By now you have a picture in your mind of how this landscape floods. In the space provided below, write a description of this landscape so that someone who had not seen it flood before could imagine it flooding in their mind.

Landscape flooding description:

4. Try to envision walking from G to H., especially when you are going up hill and when you are going downhill. Sketch the profile from G to H in the space provided.

Profile from G to H:

Part 3. Examining the Harrisonburg Quadrangle topographic map

1. What is the relief (in feet) of Massanutten Mountain? Relief is the difference in elevation between the highest and lowest points in a region. (How can you easily identify the highest peak of this mountain?)

2. What is the latitude and longitude of Massanutten Peak? (Interpolation between provided reference latitudes and longitudes along edge of map is key.)

Latitude =

Longitude =

3. What is the distance of the stream that flows from Massanutten Mountain to Massanutten Caverns? (Think - how can you measure this curved feature?)

Distance in feet:

Distance in miles:

4. What is the gradient of the stream that flows from Massanutten Mountain to Massanutten Caverns? Gradient = how steep or gentle the slope is. From math classes remember that slope = rise/run. The units are typically feet/mile or meters/kilometer.

Qualitative description:

Quantitative measurement:

5. Describe the shape of the contour lines as the cross the stream you examined in #3 & 4. Specifically relate this pattern to the flow direction (e.g., downstream, upstream) of the stream.

This pattern can be generalized for all streams on topographic maps and is useful to quickly determine the flow direction of a stream.

6. Try envisioning walking in a straight line from Massanutten Caverns up to the top of the ridge (let’s say to the “M” in the word Massanutten printed along the ridge). Sketch the profile of the topography you would transverse.

7. The profile you just sketched can be drawn more accurately and to scale by using the elevation information that the contour lines provides along the transverse. Use the index contours only and the attached graph paper to plot a profile that is to scale.

Commonly in order to show surface topography in its true relationship (true to scale) to horizontal distance a profile has the same vertical and horizontal scale. But, if horizontal distances of the area in interest are so great relative to the relief (vertical difference in elevations) then we often exaggerate the vertical scale. The resulting profile would have vertical exaggeration (V.E.).

What is the vertical scale of your profile?

What is the horizontal scale of your profile?

Is there vertical exaggeration? You can calculate the V.E. in the following way:

. VE = Distance of one horizontal unit

Distance of one vertical unit

For example, if 1 unit on horizontal scale = 250,000 units in real life and 1 unit on the vertical scale = 10,000 units in real life then:

VE = 250,000 = 25X10,000

8. The town of Harrisonburg decides to build a new dam and reservoir for recreation and flood control. The proposed dam location is marked as a dark thick line on the attached photocopy of part of the Harrisonburg Quadrangle. (Refer to your original map to see the colors, but write only on the photocopy.) If the top of the dam came to an elevation of 1300 ft above sea level and the reservoir filled with water to the very top of the dam, shade in the land that would be covered with water. (How will the general rule about contour lines and stream flow direction from #5 help you here?) Would part of Main Street be flooded?*

9. I live on the east side of Massanutten Mountain - just to the east of this topographic map. What is the name of the map I would need to obtain if I wanted to locate my house? (Can you determine 3 ways I could find the right map?)

*adapted from an exercise in the JMU Geology 110 lab manual.Part 4. Finding the topographic map of your home

This part of the activity is specifically tied to Project 3 of the course – your environmental site assessment of your home.

http://www.terraserver.com/search/search.asp

1. Using teraserver.com find and print the topographic map of your home. You can often use your specific street address in the search. If the search does not bring up your home try abbreviating your street (e.g., High St rather than High Street).

2. Provide a description of the landscape shown:

3. What other imagery is available for that location?