Interpretation and Construction of Topographic Maps

1. Interpretation and Construction of Topographic Maps

2. Goals of the Topographic Map Interpretation Lab • Understand how surface features are expressed on • the earth’s surface • Observe a 2-dimensional map and “convert” it to a • 3-dimentional relief map • Locate geographical positions using the PLSS system • (a legal description) • Students will understand the nature of contour lines • and how contour lines can determine: • surface features • river gradients • map relief and elevation • Develop skills that enable the student to construct • topographic maps and topographic profiles 1st Lab 2nd Lab

3. Topographic Map Lab • Types of maps • Planimetric Maps – a typical road map with cities • Topographic Maps – a planimetric map as well as a 3-d representation of the • “lay of the land” converts a 2-D to a 3-D map Shows streets, roadways “sometimes not very accurate” elevations Shows accurate scaling, elevation and geographic locations.

4. What can one do with a Topographic Map • Calculate river gradients • Hiking- how rigorous is the trail • Hunting – where would game hang out? • Navigate your way • Interpret various geological features One cannot live without topographic maps !!!

5. Interpreting SCALE on a topographic map • Representative Fraction Scale (RF scale) • Graphic Bar Scale (graphical representation) • Verbal Scale (what does the map say?) feet 50 100 150 200 Model (Map size) Actual Size 1:18 scale 1:1 scale Graphically shows distance “What is the map telling you???”

6. Representative Fraction Scale (RF scale) the “ratio scale” or “unitless scale” 1 : 24,000 or 1/24,000 – can apply any units (:) or (/) means equal (=) How does this scale work? (let’s use inches and the scale of 1:24,000 1 map inch = 24,000 real earth inches OR 1 map inch = 2000 feet OR 1” = 2000 feet Which scale shows more map detail? 1:24,000 1:5,000 1:1000 1:525,000

7. Graphic Bar Scale:graphical representation of distance 2 1 3 4 0 Kilometers 0 4 Comparing a map distance (from point A to B) to the Bar scale (at the bottom of map) What about a meandering river??? STRING

8. The Verbal Scale: • The map “tells” you what the scale is • (just listen?) • Usually located at the bottom of the map • ALL verbal scales should match the • RF scale and bar scale • Example: • 1 inch equals 2000 feet

9. MD TN Map Symbol MN Map Orientation – Where does your compass point ???? Magnetic Declination: True North (Santa Claus) vs. Magnetic North Magnetic Declination (MD) North (Santa Claus) Map points to TN X Bakeo Compass needle points to MN EARTH The angle between TN and MN is the magnetic declination

10. NEWS North MAP East West South

11. Townships North/South 6 5 4 3 2 1 7 8 9 10 11 12 18 17 16 15 14 13 19 20 21 22 23 24 T2N R2W T2N R3W T2N R1W T2N R1E T2N R2E T2N Ranges East/West T1N R1E T1N R3W T1N R2W T1N R2E T1N R1W T1N Base Line T2N, R2E T1S R2W T1S R3W T1S R1W T1S R2E T1S R1E T1S R2E R3W R2W R1W R1E Principal Meridian 6 miles 1 mile 30 29 28 27 26 25 NW ¼ of NE1/4 NE 1/4 of NE 1/4 31 32 33 34 35 36 NW 1/4 6 miles SW 1/4 of NE 1/4 SE ¼ of NE 1/4 X Sections 1 mile 20 SW 1/4 SE 1/4 T2N,R2E,Sec 20,1/4NE,1/4SW

13. Creating a Topographic map with Contour Lines 40 40 40 40 Contour line – a line that connects points of equal elevation equal points of elevation 5 important rules of contour lines • Contours line do not cross or divide • 2. Contour lines will eventually close – they don’t stop • 3. Steep slopes – contour lines are close together • Gentle slopes – contour lines are widely spaced • 4. Depressions shown with hachures pointing downward • 5. Contour lines intersecting streams will always “V” • in the upwards direction (streams flow through the open • “V”)

14. Contour lines never cross or divide 200 100 Contour lines eventually close – Don’t stop 500

15. Close together contour lines = STEEP SLOPES Separated contour lines = GENTLE SLOPES Steep Gentle

16. Depressions are shown with hachures pointing inward Rivers always flow in the direction of the open “V” of a contour line NORTH WEST

17. The Contour Interval 300 Contour Interval = 20 CI = 20 200 500 Contour Interval = 100 CI = 100 100 How many contour lines can fit in a determined Space??? The Index contour line – the “dark numbered” elevation line The contour interval – the amount of contour lines in-between the index contour lines

18. Calculating the gradient • how steep is the slope?? Higher slope # = steeper Rise Run Rise = highest elevation – lowest elevation Run = the length (distance) Rise and Run MUST be in the same units preferably “feet”

19. Making a Topographic Profile • represents a “cross-section” or side view of • topography • uses a horizontal and vertical scale • gives the map reader a “picture” of the “lay of • the land”. How do you make a Topographic profile ?

20. Lay a strip of paper over the topographic area • “Mark off” contour lines that intersect the paper • strip – recording their elevations Intersecting contour lines

21. Remove strip of paper and place it on graph • paper – plot elevation points (on strip) to • match vertical scale elevation points potting points on the graph paper Strip of paper

22. Outline the topography by “connecting” the • dots --- Use your artistic ability to construct • a “smooth” picture

23. B E D C F A