Chapter 5

Laboratory Manual for Physical Geology, 3rd edition

Solutions

Pre-Lab Questions

TOPOGRAPHIC MAPS

Answer the following questions from information presented in this chapter.

Quadrangle - A mapped section of the earth’s surface which is bounded by lines of longitude and latitude.

2. Describe latitude and longitude lines and give the base line (zero degree line) for each.

Latitude – angular distance from the equator measured north or south --Lines of latitude vary from 0o - 90o north and 0o - 90o south. Latitude lines are called parallels.

Longitude - angular distance measured east to west from the Prime Meridian which is 0o longitude -- Longitude lines are called meridians. They range from 0o - 1800 west and east.

 The coordinates of point B are: 40oS, 20oW Remember your direction and that latitude should always be expressed first.

3. How are degrees of latitude and longitude subdivided?

Minutes (‘) and seconds (“)

There are 60 minutes in a degree and 60 seconds in a minute

4. What is meant by magnetic declination?

Magnetic declination - The angle formed between the direction of true north and magnetic north.

5. Convert the fractional scale of 1:24000 to a verbal scale of

a. one inch = 2000 feet

b. one inch = 0.38 miles (one mile = 5280 feet)

6. How do you calculate the total relief on a topographic map?

7. What is a contour line?

Contour line - a line on the map which shows and connects points of equal elevation

8. What is meant by contour interval on a topographic map?

Contour interval - the vertical difference in the elevation between adjacent contour lines

How to determine contour interval:

 From this area of a map we can see that two of the index contours are labelled 6000 and 6400, with 4 intermediate contour lines between them. This means that there are five "steps" between 6000 and 6400. 400/5 = 80, so the contour interval is 80 feet. Be sure you are comfortable with the display of contours in topographic maps, as shown at the USGS web site, and with the rules for contour lines listed in figure 9.5 on page 150. We will see an application of the "Supplementary Contour Line" in our work in lab with desert landforms. This web site has good information on contour lines and other means of depicting relief on maps.

9. How do you recognize an index contour?

Index contours - thicker and darker than normal contour lines. Every 5th contour line is an index contour.

10. In what topographic situation will contour lines merge?

Contour lines merge when there is a vertical cliff.

11. Complete the following sentences (Click on answers to reach examples):

a. Concentric, closed contours represent ____________hill_____________________.

b. Closed contours with hachure marks represent ________depression__________________.

c. When contour lines cross a stream they ______v” upstream_________________________.

12. What is meant by vertical exaggeration?

Vertical exaggeration is an expression of the relationship between the vertical scale and horizontal scale of a topographic profile. It is a means to show the features of an area that does not change greatly in elevation.

13. How is VE (vertical exaggeration) calculated?

Vertical Scale divided by Horizontal Scale.

14. How does a topographic profile differ from a topographic map?

A topographic profile (side view) shows features that otherwise would not be present on a topographic map (aerial view).