p" — 
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004 
  
narrowest place to 29 km at the widest. The width of the canyon 
indicates that it is 3 to 4 times narrower compared with the 
width of the Valles Marineris individual troughs. Most 
researchers agree that the shape of the Grand Canyon has been 
formed by a number of combined processes. The most 
important process is erosion, primarily by water and second by 
wind. 
  
meters. The elevation range is in the interval 0 to 2838 m. The 
borderline of the Canyon system was interpreted and digitized 
(Figure 4). The geomorphometric analysis will be performed 
within the area outlined in Figure 4. 
e 
  
Figure 4. The DEM and the borderline of the study area. 
2.3 Data 
The 1-degree DEM are distributed by USGS and provide 
coverage in 1 by 1 degree blocks for all of the contiguous 
United States, Hawaii and limited portions of Alaska. Figure 3 
shows the DEM that was used for the landscape 
characterization of the study area. The DEM in figure 3 was 
produced by merging 3 of the | by 1 degree blocks (figure 1). 
The majority of the 1-degree DEMs are produced from 
cartographic and photographic sources. 
The elevation data from cartographic sources are collected from 
any map with scale from 1:24000 through 1:250000. The 
topographic features as the contours, the drain lines, ridge lines, 
lakes and spot elevation are first digitized and then processed 
into the required matrix form and interval spacing. The I- 
degree DEMs consists of a regular array of elevations 
referenced horizontally on the geographic coordinate system of 
the WGS 84. Elevations are in meters relative to National 
Geodetic Vertical Datum of 1929 in the continental U.S and 
local mean sea level in Hawaii. The 1 degree DEMs have an 
absolute horizontal accuracy of 130 m, and an absolute vertical 
accuracy of 30 m. The DEM in figure 3 covers a geographic 
region bounded by longitude -144 to -111 degree and latitude 
from 36 to 37 degrees. The DEM contains 3603 columns and 
1202 rows, while the spacing is 80 m. Each sample represents 
median observed topography within a 0.0011102 by 0.0011102 
degree area. The minimum and maximum topography 
observations within the current data set are from 0 to 2838 
meters. 
The study area (located in Grand Canyon) is bounded by 
latitude 36 to 37 and longitude -114 to -111 degrees. The DEM 
contains 3426 columns and 1545 rows while the spacing is 80 
842 
2.4 Hypsometry 
A shaded relief map (sun position was in SE) and elevation 
profiles were used in an attempt to interpret the topographic 
features and the structure of the canyon (Figure 5). 
* Profiles gg' and ff" are vertical to the tributary 
canyons observed on the peneplain surrounding the 
canyon. 
e Profiles aa’,bb’, cc’, dd’ and ee’ are vertical to the 
main axis of the canyon. 
eri