Introduction to Map Use
study outline – terrain representation
You should be able to:
1. describe four different methods of terrain representation and discuss their advantages and disadvantages
A. spot heights
a. give the exact elevation of a point on a map
b. used on standard topo maps to give the elevation of peaks and lake levels
c. advantages
i. exact value of surveyed elevation
ii. don’t take up much space or clutter map
d. disadvantages
i. difficult to visual shape of terrain with just a few elevation numbers
ii. no information about shape of the landscape between spot heights
B. contours
a. lines following paths of constant elevation across a map
b. contour interval is the difference in elevation between adjacent lines
c. most useful for navigation by landform features, planning off road travel and many engineering tasks
d. drawing contour lines
i. follows the rules for isolines for displaying continuous data on any map
ii. contours form a closed loop or end at the edge of the page
iii. contours don’t cross
iv. contours can join only at a vertical cliff
v. when changing from going uphill to going down hill (or vica versa) you will always encounter the same contour level twice
vi. in all other cases adjacent contours most be one contour interval higher or lower
e. special contours
i. index contours –
1. darker contours at specific intervals representing “round number” elevations e.g. every 50 or 100 ft
2. often marked with contour elevation along the line
3. aid in determining the elevation of a point within the countours
ii. depression contours –
1. contours descending into a bowl or pit often have a special line symbol
f. enhancing contours
i. layer tints color elevation ranges on a contour map to aid
in interpretation of the landscape (e.g. 0-500 ft – dark green,
ii. illuminated contours – changing the tone of contour lines based on their relationship to slope and an imaginary light source, giving a 3-D effect while maintaining all the information of the contour lines
C. digital elevation model
a. electronic description of terrain
b. two main formats
i. raster – gives the elevation at every point in a regularly spaced grid
ii. vector – divides the surface into triangles and gives the latitude, longitude and elelvation of each corner
D. shaded relief (hill shading)
a. an artistic rendering, usually with the aid of a digital elevation model, that shows what the landscape would look like looking straight down on it with the sun at a middle elevation, usually in the upper left.
b. very useful for visualizing the landscape as it would look in an aerial photo, as a background for a map for instance
c. doesn’t allow measurement of elevations or slopes
E. physiographic diagram
a. represents major elements of the terrain on a planimetric map with artistic renderings of the feature as seen from a low oblique angle
F. block diagram
a. combination of shaded relief map or physiographic diagram with a represention of the the terrain profile along the edges of the diagram
b. especially useful for showing structural features in the rocks under the surface