Elevation and Elevation Profiles
A. Branscomb
Hypsology
Based on U.S. Geological Survey,32 U.S. Forest Service, and U.S. Bureau
Hypsology is the study of the relative altitude of places. Map 3 on the
of Land Management digital sources contained in an archive managed by the
facing page is a hypsometric “hill-tint” in which elevation is depicted
Oregon Geospatial Data Clearinghouse,33 Map 3 was constructed from a digi-
through variations in color and brightness. The shading is rendered as if the
tal elevation model made by joining approximately 300 individual 7.5 minute
image were a topographic relief map illuminated by a source of light at 45
quadrangle digital elevation models. Each of these is a rectangular matrix of
degrees above the map in the northwest corner, 315 degrees azimuth. It dif-
elevation values spaced 98.4 ft apart (30 m). Vertical accuracy varies from
fers from true illumination in that higher features closer to the light source do
+/- 24.6 ft (7.5 m) to +/- 49.2 ft (15 m) and horizontal accuracy conforms to
not cast shadows on those behind. No vertical exaggeration is applied.
U.S. Geological Survey national map accuracy standards, which at this scale
means that 90% of values lie within 39.4 ft (12 m) of actual location.
2000
W'
1500
Portland
(0 m)
1000
Salem
(34 m)
Oregon City
(0 m)
500
Lowell
(212 m)
Eugene
(122 m)
Corvallis
(58 m)
Oakridge
(345 m)
Elevations are at river level;
distances are along channel.
W
0
0
50
100
150
200
250
300
McKenzie R.
(290 m)
2000
400
450
A'
S. Santiam R.
(260 m)
Willamette R.
(15 m)
1500
350
1000
Beaverton
(58 m)
A
500
Headwaters
Middle Fork Willamette R.
(1284 m)
Elevation (m)
0
A
0
50
100
150
200
250
W
2000
Molalla R.
(108 m)
Willamette R.
(23 m)
1500
1000
S. Yamhill R.
(37 m)
C
500
Clackamas R.
(332 m)
Unit Equivalences
Timothy Lake
(984 m)
Metric
C'
Woodburn
(56 m)
0
0
50
100
150
Horse Cr.
(871 m)
2000
Cougar Res.
(518 m)
1500
1000
Veneta
(122 m)
200
B'
Eugene
(128 m)
0
0
50
50 m
100 m
500 m
1000 m
1500 m
2000 m
10 km
50 km
100 km
300 km
500 km
English
164 ft
328 ft
1640 ft
3280 ft
4921 ft
1.2 mi
6.2 mi
31.1 mi
62.1 mi
186.4 mi
310.7 mi
C’
C
B’
B
N
W’
S
A’
Not to scale
B
500
100
150
Distance (km)
Figure 14. Calculating slope:
In the maps below, topographic slope is determined individually
for each 1/4 acre (30 meter x 30 meter) cell in the digital elevation
model. The slope is computed by reference to cells in a 3x3 matrix surrounding the target cell. With the elevation of edge-touching cells
given twice the weight as that of corner-touching cells, the maximum
rate of change in elevation from the target to its neighbors, and its direction, are calculated. The compass direction of this line is the topographic aspect of the target cell.
60 - 214%
31˚- 65˚
49 - 58%
26˚- 30˚
38 - 47%
21˚- 25˚
31 - 36%
17˚- 20˚
Figure 13. Willamette River Basin profiles. On the profiles above, elevations for cities and towns are derived from published sources, while
those for physical features are derived from the digital elevation model.
Vertical exaggeration is 30:1 for all profiles.
Slope is represented in two forms, percentage and degrees. Degrees measure the interior angle of a triangle in which the base is the
“run” and the height is the “rise” along the direction of maximum elevation change for the cell. Percentage slope multiplies the rise/run ratio by 100. An increasingly vertical line has degrees slope approaching
90, but a percentage slope approaching infinity as the “run” denominator goes to zero. A 45 degree slope is a 100% slope.
Degree slope = 30
Percent slope = 58
θ
WRB percent slope
12
Elevation Profile Locations
300
25 - 29%
14˚- 16˚
19 - 23%
11˚- 13˚
16 - 18%
9˚- 10˚
12 - 14%
7˚- 8˚
9 - 11%
5˚- 6˚
5 - 7%
3˚- 4˚
2 - 4%
1˚- 2˚
0 - 6%
0˚
θ
θ
Degree slope = 45
Percent slope = 100
Degree slope = 60
Percent Slope = 173
Degrees of slope = θ
rise/run = tan θ
Percent slope = rise/run X 100
WRB degrees slope
PNW Ecosystem Research Consortium
LANDFORM
ANDFORMS
123°45’00"
123°37’30"
123°30’00"
123°22’30"
Map 3. Hypsometry
123°15’00"
122°45’00"
123°07’30"
122°37’30"
122°30’00"
122°22’30"
122°15’00"
122°07’30"
122°00’00"
121°45’00"
121°52’30"
45°52’30"
45°52’30"
Projection UTM Zone 10
Scale 1:750000
10 mi
45°45’00"
0 mi
0 km
10 km
45°37’30"
20 km
45°45’00"
20 mi
30 km
45°37’30"
45°30’00"
45°30’00"
45°22’30"
45°22’30"
45°15’00"
45°15’00"
45°07’30"
45°00’00"
44°52’30"
44°52’30"
44°45’00"
44°45’00"
44°37’30"
44°37’30"
44°30’00"
44°30’00"
44°22’30"
44°22’30"
44°15’00"
44°15’00"
44°07’30"
44°07’30"
Elevation
(feet)
(meters)
0 - 20
0-6
21 - 50
6 - 15
51 - 100
16 - 30
44°00’00"
44°00’00"
43°52’30"
43°52’30"
101 - 200
31 - 61
201 - 500
61 - 152
501 - 1000
153 - 305
43°45’00"
1001 - 1500
305 - 457
1501 - 2000
458 - 610
2001 - 2500
610 - 762
2501
- 3000
43°37’30"
762 - 914
3001 - 3500
915 - 1067
3501 - 4000
1067 - 1219
4001 - 4500
1220 - 1372
4501 - 5000
1372 - 1524
5001 - 5500
1524 - 1676
43°45’00"
43°37’30"
N
43°30’00"
43°30’00"
S
5501 - 6000
43°22’30"
6001123°45’00"
- 6500
6501 +
1676 - 1829
43°22’30"
1829 - 1981
123°37’30"
123°30’00"
123°22’30"
123°15’00"
123°07’30"
123°00’00"
122°52’30"
122°45’00"
122°37’30"
122°30’00"
122°22’30"
122°15’00"
122°07’30"
122°00’00"
121°52’30"
121°45’00"
1982 +
Willamette River Basin Atlas
2nd Edition
13
34