|Grayscale North America Shaded Relief – 1
What this map layer shows:
The shape of the land surface of North America, in gray and at a
resolution of one kilometer.
Also available is Grayscale United States Shaded
Relief - 200
elevation data constitute a global digital elevation model with
elevation values measured approximately 1 kilometer apart. Each grid
cell in the model has a value that represents the average height above
sea level within that cell. The Grayscale North America Shaded Relief - 1
Kilometer Resolution map layer was developed from GTOPO30 data.
The three-dimensional appearance of this image was achieved by determining
a gray tone at each point, calculated from the steepness of the slope
combined with illumination as if there were a light source in the northwest.
The height is exaggerated ten times. The exaggeration factor applied
to elevation data in the calculation of shaded relief is necessary to
add depth so that features can be seen clearly, but it can be misleading.
For example, shallow stream valleys can look like steep canyons. In general,
grayscale shaded relief can make flat-to-moderate landscapes appear more
rugged than they really are.
Production of this map layer was part of a collaborative effort led
by staff at the U.S.
Geological Survey Center for Earth Resources Observation and Science (EROS). This center archives, processes, and distributes
remotely sensed data, including elevation data at various scales, and
works with agencies and organizations around the world to support studies
using remotely sensed data. Small-scale elevation data are used for a
wide variety of applications, including landscape visualization, hydrologic
modeling, and geologic studies.
The Grayscale North America Shaded Relief - 1 Kilometer Resolution map
layer is a shaded-relief image showing the terrain of most of North
America. This map layer shows the general nature of the landscape in
a visually dramatic way but does not portray elevation values. From
the grayscale shaded relief image there is no way to tell how high
or low an area is and precise measurements of slope or aspect cannot
be made. The original GTOPO30 data must be used for conducting analysis
and determining elevation values.
The National Atlas also includes a 200 meter resolution
grayscale shaded relief map layer that covers the United States, Puerto Rico, and
the U.S. Virgin Islands.