UNIVERSITY OF SOUTH ALABAMA
GY 301: Geomorphology
Last Time
Finish introduction to topographic maps
How to do transit (compass) surveys
Lecture 3:
Constructing Contours
Map Coordinate Systems
Land Office Grid System
R2W R1W
R1E
6 miles
R2E
• Land Office Grid system (Township & Range)
• Universal Transverse Mercator (UTM)
• State Plane Coordinate System (SPCS)
6
T2N
T1N
State Capital
5
4
3
2
1
7
12
18
13
T1S
19
24
T2S
30
25
31
36
36 square
miles
NW
NE
SE
Legal description of location:
NE ¼ , SW ¼, section 22, T2S, R2E
Target location
The Pocket Transit (Brunton)
• Used to measure compass directions
• Allows for magnetic declination correction
• Can measure vertical angles with clinometer.
Distributing Closed Traverse Error
• Error is distributed cumulatively through closed
traverse
4
3
6
7
5
2
1
original
9
8
Total error vector
http://wb8.itrademarket.com/
1
Distributing Closed Traverse Error
Today’s Agenda
• Error is distributed cumulatively through closed
traverse
A Simple day;
1. How to draw contour lines
2. Computer contouring methods
5/9 error
vector
2/9 error
vector
4
6
3
7
5
1/9 error
vector
2
1
8
9
original
corrected
Total error vector
Contouring
Contouring
Before starting….
•163
•155
•174
•102
•170
•103
•150
•163
•125
•143
•158
•117
•138
•Locate the highest and
lowest areas
•What system are the
spot elevations? (feet)
•What is the required
CI? (contour interval)
•155
•174
•get a “feel” for the
map.
•135
•162
•184
When starting….
•163
•102
•135
•170
•184
•162
•103
•150
•163
•125
•143
•158
•146
•127
•133
•127
•120
▲ 130
•140
CI=20 feet
•162
•103
•150
•163
•125
•143
•158
•120
™- contour lines connect points of equal elevation
•102
•135
X •184
▲ 130
Contour Maps (summary)
When starting….
•155
•174
•133
CI=20 feet
Contouring
•170
•117
•138
•146
•140
•163
•Use pencil
•Light pressure
•Start at highest
elevation, one line
at a time
•138
•117
•Use pencil
•Light pressure
•Start
at
the
highest elevation
• do one line at a
time
•Proportionality
rule for contour
spacing
•146
•127
•140
•133
▲ 130
•120
Chalk Board
CI=20 feet
2
Contour Maps (summary)
™- contour lines connect points of equal elevation
™- steep slopes are shown by closely spaced contour lines
http://www.armystudyguide.com/content/SMCT_CTT_Tasks/Skill_Level_1/land-nav-task-6-determine.shtml
Contour Maps (summary)
™- contour lines connect points of equal elevation
™- steep slopes are shown by closely spaced contour lines
™- gentle slopes are shown by widely spaced contour lines
™-contour lines do not intersect, branch or cross, except in a
vertical or overhanging cliff.
Contour Maps (summary)
™- contour lines connect points of equal elevation
™- steep slopes are shown by closely spaced contour lines
™- gentle slopes are shown by widely spaced contour lines
http://www.armystudyguide.com/content/SMCT_CTT_Tasks/Skill_Level_1/land-nav-task-6-determine.shtml
Contour Maps (summary)
™- contour lines connect points of equal elevation
™- steep slopes are shown by closely spaced contour lines
™- gentle slopes are shown by widely spaced contour lines
™-contour lines do not intersect, branch or cross, except in a
vertical or overhanging cliff.
™- when contour lines cross streams they bend upstream; the
contour line forms a 'V' with the apex at the intersection with
the stream, and pointing in an upstream direction (law of the
V’s-mach one). Beware low gradient streams!
http://www.the-fitness-motivator.com/images/contour-lines.jpg
Contour Maps (summary)
™- - closed contours appearing on the map as ellipses or circles
represent hills or knobs.
http://www.armystudyguide.com/content/SMCT_CTT_Tasks/Skill_Level_1/land-nav-task-6-determine.shtml
Contour Maps (summary)
™- - closed contours appearing on the map as ellipses or circles
represent hills or knobs.
™- closed contours with hatchures, short lines pointing toward
the center of the closure represent closed depressions.
http://homework.syosset.k12.ny.us/teachers/sbostrom/depress.jpg
3
Computer Contouring
™Several different software options are available (Surfer,
AutoCAD, etc).
Computer Contouring
™Several different software options are available (Surfer,
AutoCAD, etc).
™All permit “rapid” contouring and offer nice options (e.g., 3D
colourization of maps
http://www.3dfmaps.com/h3.gif
Computer Contouring
™Several different software options are available (Surfer,
AutoCAD, etc).
™All permit “rapid” contouring and offer nice options (e.g., 3D
colourization of maps
™Most are rather expensive
(e.g., AutoCAD), but not
always (e.g., Google Maps)
Computer Contouring
…but once learned, permit repetitive
assessment/revision of maps sheets and
data sets (e.g., a component of GIS)
Computer Contouring
™Several different software options are available (Surfer,
AutoCAD, etc).
™All permit “rapid” contouring and offer nice options (e.g., 3D
colourization of maps
™Most are rather expensive (e.g., AutoCAD), but not always
(e.g., Google Maps)
™Most are not so user friendly (e.g., AutoCAD)…
Upcoming Stuff
Homework
Finish lab 1 (due Friday)
Next Lecture:
Making Topographic Profiles
Friday’s Lab:
Outside: determining elevation differences (Teams Again)
4