LabFourF20Online

Name _________________________ Lab Four: Topographic Maps, Isolines and Contours Since maps display geographic data, this lab is designed to introduce you to an important method for displaying information on maps- isolines. Isolines are special lines used to connect points of equal value. For example, U.S.G.S. Topographic Maps use contour lines to connect points of equal elevation. Isolines are also used on weather maps to show temperatures (isotherms) and atmospheric pressure (isobars). Contour lines give insight into the topography (difference in relief) of an area without needing a three dimensional model. Materials: Color Pencils or Paint program Screen Capture Software Lab 4 Online Map Objectives: • Identify features on standard U.S. Geological Survey topographic maps. • Interpret & construct isolines • Determine elevation using contour interval • Assess gradient based on contour line spacing • Identify landforms based on contour line patterns Part 1: Interpreting and Constructing Isolines Basic characteristics of isolines:  Isolines are closed lines having no ends. Note: The line may close outside the margins of the map.  Isolines represent gradations in quantities so they very rarely touch or cross.  Isolines are drawn at regular intervals (numeric difference between one isoline and the next). If more than one interval is used on the same map, a different line symbol will be used to display those lines having different intervals.  How close together the isolines are drawn depends on the gradient (change in the interval). Isolines drawn close together indicate a rapid horizontal change in the interval (steep gradient). Whereas, isolines drawn far apart, indicate a gradual horizontal change in the interval (gentle gradient).  Values inside a closed isoline are either higher or lower than those outside the closed isolines. Cartographers use isolines to make it easier to interpret what otherwise would appear as random data points. Look at Diagram A below; at first glance it seems like randomly place elevations points (expressed in feet). It isn’t until isolines are drawn that an elevation pattern emerges (Diagram B). Note that the elevation incresases as you travel from the right side of the map to the left side. The process by which isolines are constructed is called interpolation. The Interval displayed below is 100 feet. 1

Exercise 4.1: 1. The map below shows temperatures (F ⁰ ) across the United States. The goal of this exercise is to draw isotherms in 10 ⁰ increments . Step 1- Classify the Data Using colored pencils or the Paint program on your computer, lightly circle each data point according to the key below. 70 ⁰ - 79 ⁰ = Red 60 ⁰ - 69 ⁰ = Pink 50 ⁰ - 59 ⁰ = Orange 40 ⁰ - 49 ⁰ = Yellow 30 ⁰ - 39 ⁰ = Green 20 ⁰ - 29 ⁰ = Blue 10 ⁰ - 19 ⁰ = Purple Step 2- Draw isotherm lines in BLACK. Start by locating 70 ⁰ - draw a line representing the 70 ⁰ contour line. Values higher than 70 ⁰ should be on one side of the line and values lower than 70 ⁰ should be on the other side. Repeat this process every 10 ⁰ . I suggest using a pencil first or if using a Paint program, save before drawing each isotherm. Step 3- Color the Bands. Using the colors on the key, color the bands between the contour lines. Optional: If you want to recreate this map on the computer instead of printing it out, download the IsothermsColor.png from Canvas. 2

 Contour lines crossing ridges always bend down slope creating “U”s. In other words, the U always points towards the lower elevation. We used the Mt. Whitney Topographic Map in Lab 2. Here is a portion of that map surrounding Lookout Mountain.  The contour interval of this map is 80ft.  The elevation of Point A is 7360 ft.  Point B is in a depression . The estimated elevation at the bottom of the depression is 7960 ft. The depression is between 8000 ft and 8080 ft contours. The lip of the depression matches the lowest elevation: 8000 ft. The bottom of the depression is estimated at ½ a contour interval lower than the lip.  The peak of Lookout Mountain is marked with an X. The elevation is noted as 8352 ft. The west side (left) is steeper than the east side (right). You can tell by the spacing of the contours. They are much closer on the west side than on the east side.  The blue dashed lines are streams . Notice that the contours are V shaped and point up towards higher elevation. In between the two streams in Section 31 is a ridge . Notice how the contours are U shaped and point to lower elevation. 4

Exercise 4.2: Use the hypothetical contour map below, answer the following questions.  North is at the top of the map.  Streams are shown as dashed lines  Elevation is noted in feet. 5

Exercise 4.3: Open the Lab 4 Digital Map and answer the following questions. Go to the Mirror Lake Bookmark. 1. The green pushpin is on Reid’s Peak. Zoom in and look at the contours. Draw an example of the contour lines that illustrate a peak (mountain top). 2. If you were standing on Reid’s Peak, can you see the Red pushpin (Point A)? Explain your answer. 3. This summer I hiked to the top of Bald Mountain (Blue line). The trial started at approximately 10,800 ft. What was the difference in elevation from the trailhead to the peak? 4. Based on the spacing of the contours, which is steeper? The section from Point B (blue pushpin) to Point C (purple pushpin) OR Point C to Point D (yellow pushpin) 5. The section of the trail from Point C to the Peak is a ridge. How would you describe a ridge? What do the contour lines look like that illustrate this feature? Draw an example. Go to the Chino Hills Bookmark. 6. I often hike in Chino Hills State Park. If I start my hike at the green pin and walk to the red pin, am I going up hill or downhill? What is the elevation at the start of the route? What is the elevation at the end? 7. What is the elevation of the white pushpin? You may have to zoom in a little. 8. The dashed blue line represents a valley in which an intermittent stream would run. Zoom in and look at the contour lines. Describe the pattern observed and draw an example. 7

9. Take a screen shot of this area and draw in the location of two more intermittent streams. Insert image here: 10. Take a screen shot of a peak in the Chino Hills area and insert image here: Go to the Menan Butte Bookmark. 11. The blue push pin sits instead a depression. Notice how the contour lines in a depression look different from those on a peak. Draw an example of a depression contour. 12. What is the estimated elevation at the bottom of this depression? Challenge Problem (this is an optional problem) Do you like to hike? If so, in the Lab 4 Online map, locate the area you typically like to explore. Take a screen shot of the area showing the contours. Do the contours match the landscape you are used to seeing? In other words, can you point out a peak on the screen shot or a steep or gentle part of the trail? Does your typical path follow a ridge line or a valley? 8