GSC 1530

1. GSC 1530 Pace and Compass Mapping Exercise

2. Introduction • Today you’ll learn basic orienteering and how to make a crude map • The type of map you’ll make was commonly used to record mining and property claims, especially in the western U.S., during the 19th century before more advanced surveying equipment was invented 1822 Michigan Territory Map

3. Introduction • The orienteering and position plotting skills you’ll learn are still very useful, especially if you enjoy hiking, hunting and boating • Remember: modern GPS (Global Positioning System) equipment may not always function properly!

4. Introduction • Although many types of information can be displayed on maps, the primary purpose of any map is to locate points (position) • Our technique for locating points: “Distance and bearing from a prominent marker”

5. Introduction • We’ll measure the distance between points on our traverse via pacing • We’ll measure the bearing (orientation) between points on our traverse via the compass

6. Pacing • Prior to going outside, determine your pace length by walking the 50 foot (ft) course in the hallway • Use a consistent technique for counting your pace number • Divide the 50 ft length by the number of paces to obtain your “feet per pace” value (calculate to two decimal points) • Example: 50 ft/23 paces = 2.17 ft/pace

7. Pacing • To calculate the distance between two points on your traverse: multiply the pace count by your previously determined pace length • Example: assume a 2.80 ft/pace value; How far did you walk if you counted 100 paces between two points? • Visualize: 100 paces x 2.80 ft/pace = 280 ft

8. Pacing • Each person conducts their own pacing • Outside, make sure you maintain the same pace length you walked in the hallway and walk a straight line path between each set of points on your traverse

9. Obtaining Bearings • You and a partner will share a Brunton quadrant compass • Open the compass and inspect its basic components with me (switch to document camera)

10. Precautions • Make sure you read the correct end of the needle (letter N end or white end, depending on the type of compass you possess) • Strive to hold the compass horizontally level (at least 1/3 to 1/2 of the bubble resides within the “bull’s eye”) • Remember: your compass needle must be free to align itself with the Earth’s magnetic field

11. Procedure for Sighting a Bearing • Hold compass at waist level as seen in the following figure, use the adjustable mirror and sighting arm (pointed toward object of interest) to align object in the compass mirror (see figure)

12. Look into mirror; sight object of interest. Visually extend the line bisecting the compass mirror through the object of interest. Adjust the mirror and sighting arm as necessary. Hold compass level. Close one eye (consistently) to reduce parallax. Take reading when needle stops moving.

13. Procedure for Sighting a Bearing • All readings on a quadrant compass are recorded using the North (represented by the star) or South pole positions (00) as reference points • Don’t fret about the reversal of the East – West designations • You record how many degrees east or west of the pole positions the “reading end” of the compass needle points; e.g., North 60 degrees west (N 600 W) or South 30 degrees east (S 300 E) • You should be able to record bearings to a precision of 10 • Switch to document camera for more examples

14. Further Precautions • Does the “reading end” of your compass needle point toward the Earth’s magnetic north or geographic north pole? • Why then does the north arrow on a common map point toward the geographic north pole? (see slide)

15. 12/26/05 The magnetic north pole has shifted location about 685 miles in the last 150 years (Joseph Stoner, Oregon State University)

16. Further Precautions • Because the magnetic north pole position fluctuates, we must be able to correct our compass bearings to geographic bearings • The variation in bearing between the north geographic and north magnetic pole is called the declination – it is measured in degrees and direction

17. Further Precautions • Your position on the Earth’s surface determines the declination values • Worldwide, declination maps are periodically revised so we can correct our magnetic compass readings appropriately (see figures)

20. Understanding Inclination and Declination

22. Further Precautions • We’ll assume therefore a magnetic declination of approximately 7o West (2007 MI Aeronautical Chart) • Prior to your arrival I corrected our compasses for the local magnetic declination • Important: if your compass was properly corrected for magnetic declination, then the bearings you record are geographic bearings – you’ll use these same bearings for plotting your map

23. Further Precautions • Let’s verify the magnetic declination correction on your compass – the tip of the zero pin should point approximately 7o to the right of 0 (switch to document camera)

24. Your traverse • You will map the relative positions of seven lamp posts marked with colored flagging tape in the field between B, C, T and G buildings (see figure)

25. You may start your closed loop traverse • at any lamp post • Walk in either a clockwise or counter- • clockwise direction • Record the bearing (consensus) between • successive posts on your traverse; each • partner records their pace count between • the posts • Carefully record your bearings and pace • count information • Finish your traverse at the origin • point (walk a closed loop) = lamp post marked with colored flagging tape

26. Plotting Your Map • First convert your pace counts between lamp posts to land distances and then map distances • We’ll draw our map using a scale of 1 inch = 50 feet (1 inch on the map is equivalent to 50 feet on the ground surface) (see board example) • Be careful when converting calculator decimal values to map measurements if your ruler subdivides each inch into sixteenths • Example: 3.5 inches (calculator) = 3 5/16 inches (ruler)

27. Plotting Your Map • Two methods for proper conversion of the calculator decimal component to sixteenths of an inch: e.g., 3.5 inches: cross-multiply; 0.5 = 5/10, 5/10 = x/16, 80 = 10 x, x = 8 • Or, multiply the decimal component by 16; 0.5 x 16 = 8 • So 3.5 inches (calculator) = 3 8/16 inches (ruler)

28. Plotting Your Map • Place a geographic north arrow and scale (verbal and bar) on your map • Place your initial lamp post point on your map sheet (with forethought) as a “prominent marker” • Use the protractor to determine the bearing between successive lamp posts, use the calculated map distances to determine the offset between the lamp posts (see figure)

29. N 1 inch = 50 feet (ft) 1 0 50 ft

30. Plotting Your Map • The protractor will be used to mimic (one hemisphere at a time) the face of your compass • Mentally (or physically) replace the protractor’s numerals with those seen on the compass face (switch to document camera)

31. Plotting Your Map • To plot the traverse points: • 1) Place the protractor’s center point atop the prominent marker point; align the protractor’s vertical axis parallel to the map’s north arrow • 2) Determine the bearing orientation between the prominent marker and the next lamp post on your traverse • 3) Place the next point, along this bearing, the calculated map distance between the two posts (view document camera example) • 4) Repeat this procedure until you plot all seven lamp post positions; flip the protractor’s orientation to plot southerly bearings

32. Important Note • Your map will actually contain 8 points representing the 7 mapped lamp posts • Two number one points will appear – the one you placed on the map as the initial prominent marker and the number one point fixed on the map when you plotted the distance and bearing data gathered on your traverse from lamp post seven back to lamp post one (see figure)

33. N Error of closure 1 inch = 50 feet (ft) 1 0 50 ft

34. Important Note • The error of closure is one measure of the accuracy of your mapping • An error of closure < 35 ft is reasonable for a first mapping attempt

35. Addendum - Triangulation • You’ll also determine the location of another lamp post (marked with a different colored flagging tape) via a technique called triangulation • This is the same technique used in the GPS system • No pacing is utilized; your position is located by taking bearings to three (tri) known points • This technique is particularly helpful if you are uncertain of your location (see figure)

36. Numbers equal ground elevation above sea level Sight bearings to three known map points Known point 3 Known point 2 Known point 1

37. Triangulation Directions • After you finish gathering data for the closed traverse, locate the triangulation lamp post (It lies within the closed traverse boundaries.) • Sight bearings to three carefully chosen lamp posts on your traverse • FROM those lamp post points on your map draw bearing lines that are opposite (reverse) of the readings you recorded • The exact, or approximate, intersection of the three bearing lines locates the triangulation point (see figure for further explanation)

38. Example: if you sighted a N 300 E bearing TO your post number four, then you draw a S 300 W bearing line FROM post number four N Reverse bearing line Error of closure 1 inch = 50 feet (ft) 1 0 50 ft = triangulation point

39. Final Comments • Each person submits a finished map • Your final map contains: a north arrow, scale, closed traverse points (plus error of closure point), the triangulation point (label) and your name • On the rear of your map sheet, answer (complete sentences) the questions on the second page of your instructions handout (number 8). • Good luck!