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6.2: Activity 1 - Survey Techniques

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    74771
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    Amanda Wolcott Paskey and AnnMarie Beasley Cisneros
    Cosumnes River College and American River College

    Part 1. Using a Compass

    Before the development of GIS (geographic information system) and GPS (global positioning system), a compass was the only reliable method archaeologists could use to locate a site precisely. This exercise will familiarize you with the basics of how a compass works, how you can find and read bearings, and how to triangulate to pinpoint your exact location on a map.

    You will work in groups of no more than four people, and each of you will need to calculate your stride length. We will perform a short exercise to help you calculate your stride length before we begin using the compasses.

    Your instructor will provide you with a compass to use for this activity. Do not use a compass app on your phone!

    Your instructor will teach you the basics of compass operation and use.

    Practice finding the following directions (bearings), which you’ll do by first moving the dial appropriately and then moving your body so all the arrows align.

    • 30 degrees
    • 90 degrees (east)
    • 270 degrees (west)
    • 310 degrees

    Part 2. Calculating Stride Length

    You’ll need to know the length of your stride—the distance you cover when you take two steps—to measure distances accurately when working with a compass. Of course, you don’t need to know your stride length if you carry around a meter tape or are always walking near something pre-measured like a football field. But, how often do you do those things?

    When calculating your stride, be sure to wear shoes that have backs (no flip flops!) and walk at your normal pace. Don’t try to speed up or slow down since you are calculating the length covered by your normal walking style—the one you do every day without thinking.

    You will need to measure your stride against something so go to a place where you can determine exactly how far you have traveled, such as a track or football field with markings, or use a 50-meter tape measure laid out in an open space.

    Walk the predetermined distance (your instructor will tell you how far) and count how many steps you took. You will then divide the distance you covered by the number of steps. For example, let’s say you took 26 steps to cover a distance of 20 meters (m). Your step length is 20m/26, or 0.77m.

    A stride is the equivalent of two steps. If you were going to walk this same distance again, you would need to take 13 strides (26 steps/2). To compute your stride length, double your step length (0.77m*2 = 1.54m). The average stride is usually around 1.5 meters but can vary with height.

    After calculating your stride, if you find that your stride length is under 1 meter, please recalculate as this is highly unlikely.

    Now that you know your stride length, how many strides would it take for you to travel 5 meters? How many steps would it take?

    Part 3. Applying Compass Skills and Stride Length

    You will work in groups of no more than four people.

    Part A – Activity Directions

    Each group will be given a map of the campus, a compass, and a sheet of paper listing compass bearings and the distance in meters to a series of locations. You will know you have correctly found each location because it will be an unmovable object in your path (e.g., a flag pole, table, or garbage can chained to a tree). After finding the first point, you will follow the next bearing instruction in sequence to locate subsequent points (3–5 total).

    The final point for each group will be near a central location that your instructor will identify before you begin.

    Trace your route on the provided map, indicating approximately where each point was located.

    Important NOTES:
    All measurements start and end on walkways, not in planter beds or grassy areas, although you may have to go around landscaping to arrive at your intended location. DO NOT walk through planting areas. You must walk around them (keeping your compass bearing in mind and approximating how many paces you would have used had you traveled directly through the planting area (“as the crow flies”). Many signs, light poles, and other metal objects are strongly magnetic and could cause problems with the compass; be careful and avoid getting too close to any metal object.

    Part B – Activity Directions

    When you reach the vicinity of the central meeting point, you will be given three bearing locations and descriptions of the objects those bearings identify. Using triangulation, you will determine the exact location where the three bearing readings were taken and mark it (as precisely as possible) on your map.

    Triangulating a position:

    1. Use the three descriptions of features and their associated bearing readings provided to you.
    2. Holding your compass, sight bearings to each feature, changing position until your bearing reading matches the given bearings provided by your instructor.
    3. Using a ruler or the side of your compass as a straight edge, draw a long, straight vertical line through each feature. This line represents a true north (“zero”) line and will be parallel to the side borders of the map. (TIP: Set the map paper so the North arrow on the map points to true north. That way, your paper will be oriented the same way you are traveling).
    4. Using your ruler or compass as a straight edge, plot the three bearing points that were provided on the map as straight lines drawn through the features relative to the zero line. After marking the approximate locations of your readings, draw a diagonal line at the correct bearing reading for each one. Where they intersect on the map is the point at which you are standing (or the point where the readings were taken).
    5. The point of intersection of your three lines pinpoints your exact position.

    Part C – Questions

    After triangulating your position, answer the following questions as a group. Your completed map and attached set of answers to the questions are due by the end of this class session. You will return your compass and other supplies provided to your instructor.

    Assignment letter:

    Group members:

    Your name and stride length in meters:

    1. Describe each of the bearing locations in Part A (i.e. flagpole, shrub, sign, etc.). Be as descriptive as possible and be sure to mark the route and locations on your map.

    Location 1:

    Location 2:

    Location 3:

    Location 4 (if provided):

    Location 5 (if provided):

    1. Describe the triangulation point where you ended up in Part B. Be as descriptive as possible and be sure to mark the location on your map.
    1. Some directions required you to go around an object or had something in the way of your path. Describe the process you used to navigate when you were unable to walk in a straight, continuous line. How did you stay on track? How did you determine the distance occupied by the object you had to go around? How did it work out? What would have made the calculation easier (besides going through the object)?
    1. How is triangulation (either as you completed it or when finding bearing readings for three points and marking the intersection spot on your map) useful to an archaeologist working in the field?
    1. Why was it critical to know your stride length to complete this assignment?