1. Lecture 37 Reading a Topographic Map
Today we’ll practice reading a standard USGS Topographic Quadrangle map of South Buffalo
Before starting, let’s have a look at some essential map elements

2. USGS Topographic Quadrangle Map Legend
(Notice your map is not square….why?)

3. Map Scale
For example: On a 1:24000 quad map, scale factor = 24000, so a distance of 1cm on the map represents a true distance of 24000cm or 240m.
Note: Your map has been rescaled to fit on an 11’’ x 17’’ sheet of paper, so it’s no longer 1:24000! The scale bar, however, is still accurate.

4. Map Projection

5. Map Projection
The Datum: A mathematical model of the Earth (Basis for NAD83 and WGS84)

6. The Transverse Mercator Projection
Map Projection
The Transverse Mercator Projection
Tangent Case Secant Case
Yellow zone bounded by
two standard meridians and one central meridian
Secant Case
A conformal projection, meaning local angles and shapes are preserved.

7. The Transverse Mercator Projection
Each UTM zone = 6 degrees of longitude

8. Universal Transverse Mercator (UTM) Zone Coordinate System
(-,+)
(+,+)
Central Parallel
(-,-)
(+,-)
Northings
Eastings
“False
Origin”
Central Meridian
Northings/Eastings are reported in meters

9. Universal Transverse Mercator (UTM) Zone Coordinate System
Example: Easting m, Northing m (Note orange UTM grid: 1000mx1000m)

10. True North, Magnetic North, and Grid North

11. True North vs. Magnetic North
Earth exhibits a magentic field roughly analogous to a magnetic dipole
However, the poles of the magnet do not coincide with the geographic poles (i.e., the spin axis)
At any point on the planet, a compass reading (which measures the magnetic field) will show magnetic north, which in most places is offset from true (geographic) north

12. True North vs. (UTM) Grid NorthGN

13. Topographic Contours
Contours join lines of equal elevation above a datum ( ≈ sea level)
Provide a 2D representation of a 3D surface

14. Topographic Contours Landscape Perspective View (3D)
Topographic Cross-Sections
Topographic Contour Map (2D)

15. Topographic Contours
Contours join lines of equal elevation above a datum (≈ sea level)
Provide a 2D representation of a 3D surface

16. Making a topographic profile
- Any arbitrary traverse across a topographic map can be converted to
a topographic profile (i.e., a plot of elevation)

17. Topographic Contours
Resolution (level of detail) depends on contour interval; scale can be adjusted to give the desired vertical exaggeration
Elevation
Distance

18. Traverse From Map Elevation Profile Elevation (ft) Distance
860
840
820
800
780
Distance
(Scale = Map Scale)

19. Topographic Contours
Note: Both plots convey the same information, but the vertical exaggeration affects the appearance of the plot
VE=Vertical Scale/Horizontal Scale H2
Elevation
High Vertical Exaggeration H1
Distance H2
Low Vertical Exaggeration
Elevation H1
Distance

20. Surface Hydrology and Topography

21. Have you noticed a relationship between topography and watercourses (i
Have you noticed a relationship between topography and watercourses (i.e., creeks and rivers)?

22. Drainage Basins (or “Catchment Areas”)
- The “collection area” for water that falls on the Earth’s surface
- Defined above any point on a stream
Drainage Area Above Point P
Separated by drainage divides
Not fixed over geologic time
“Nested” P

23. Drainage Basins of W NY
Example of a regional drainage divide crossing the Ellicottville area

24. Ellicottville Quad To Cattaraugus Ck… To Allegheny River…
From the pattern of the streams, we can make out the regional drainage divide

25. Ellicottville Quad To Cattaraugus Ck… C B To Allegheny River… A D
From the pattern of the streams and topography, we can map surface drainage in great detail

26. A B
Elevation
Distance C D
Elevation
Stream
Stream
Distance

27. Ellicottville Quad To Cattaraugus Ck… To Allegheny River…
From the pattern of the streams and topography, we can map surface drainage in great detail

28. Stream Networks - Drainage areas evolve stream networks
-The networks are commonly characterized by their branching patterns
Drainage Area Above Point P
- Stream Order indices are used to describe the branching pattern in a network 1
1 1 1 1 2 2 3 1 3 6 P

29. Ellicottville Quad To Cattaraugus Ck… To Allegheny River… 1 1 1 2 1 13 3 1 ?
Example of Stream Ordering

30. Stream Long-Profile
Just a topographic profile that traces the axis of a stream or river ?
Elevation
Distance Downstream