TOPOGRAPHIC MAPS AND LANDFORMS
INTRODUCTION
Topographic maps are important tools in geography. They display a third dimension on 2D
maps: elevation. This is accomplished by drawing lines connecting points that display the same
elevation above sea level. These lines are called contours. This enables landforms to be clearly
displayed.
Topographic maps are not only used by geographers, you could use one to plan a hike or a
mountain biking expedition.
Elevation is not the only element you can find on topographic maps. A wealth of information
such as political boundaries, roads, railroads, bridges, buildings, surface and water features are
also displayed. For example, you can easily distinguish between vegetated and non-vegetated
areas, urban and rural areas, and so forth. These various features can be identified using a
symbols legend. A complete legend of topographic map symbols is included at the end of this
lab.
MAP DIRECTIONS AND MAGNETIC DECLINATION
Throughout this course we have and will be discussing directions: the direction the wind is
blowing from, the direction a river flows, etc.
Compass bearings show direction using the cardinal points of the compass (figure 1). This uses
letters to describe the direction in terms of N, S, E, W, or various combinations of these, e.g.,
SE, ESE etc.
Figure 1. Wind rose showing compass directions
Compasses point to the magnetic North. The magnetic North pole, located near 71°N and
96°W, attracts a magnetic compass, as opposed to True North. Magnetic north differs from the
True North because the magnetic fields of the planet are not exactly in line with the north and
south poles. On magnetic declination diagrams from the U.S. Geological Survey topographic
maps (figure 2), the star representative of Polaris, the North Star, shows the direction of the
True North centered on the north rotational pole of the Earth. MN means magnetic north. The
angle between these two lines is the magnetic declination. Magnetic declination varies with time
due to the change in position of the magnetic north (see following website for a map:
http://obsfur.geophysik.uni-muenchen.de/mag/news/e_nmpole.htm), so the date at which the
declination was measured is provided. In the United States, magnetic declination ranges from
approximately 24° east in the Pacific Northwest (Washington State) to 22° west in the northeast
(in Maine).
Figure 2. Magnetic declination (GN refers to the geographic North: the direction of a grid
line which is parallel to the central meridian on the UTM grid)
CONTOURS
An understanding of the contours on any map is possible by following a few simple rules.
1. Every point on a given contour line is of the exact same elevation; that is, contour lines
connect points of equal elevation.
2. Contour lines always separate points of higher elevation (uphill) from points of lower elevation
(downhill). One can determine which direction on the map is higher and which is lower, relative
to the contour line in question, by checking adjacent elevations.
3. The elevation between any two adjacent contour lines on a topographic map is the contour
interval. Often every fifth contour line is presented as a heavier line so that you can count by five
times the contour interval (figure 3). These heavier contour lines are known as index contours
because they generally have elevations printed on them. Whenever reporting the contour
interval it is important that the units (ft, m etc.) be reported as well.
Figure 3. Index contours
4. Contour lines can merge to form a single contour line only where there is a vertical cliff (figure
4).
Figure 4. Contours indicating a cliff
5. Evenly-spaced contour lines represent a uniform slope. Closely spaced contour lines indicate
a steep slope. Widely spaced contour lines indicate a gentle slope, i.e., the spacing of the
contours indicates the gradient/slope (figure 5).
Figure 5. Steep and gentle slopes
6. A concentric series of closed contours represents a hill or a mountain (figure 6).
Figure 6. Hill representation on a topographic map
7. Depression contours have tick marks (hachure) on the downhill side, always close, and
represent a closed depression (figure 7).
Figure 7. Depression
8. Contour lines form a V pattern when crossing streams (figure 8). The apex of the V always
points upstream (uphill).
Figure 8. Contours pattern along a river
UTM COORDINATES
The Universal Transverse Mercator (UTM) is a coordinate system based on the metric system.
The UTM coordinate system is formed by superimposing a regular square grid on each UTM
zone of 6º of longitude width (figure 9). Because there are 360º of longitude, there are 60 eastwest zones that each covers 6º of longitude. These zones are numbered from 1-60, with Zone 1
extending from 180-174ºW and continuing eastward around the globe to 174-180º E (see figure
10 for zones in the continental U.S.).
Figure 9. World UTM grid
Each UTM zone is divided into horizontal bands spanning 8º of latitude, except for the
northernmost band, which spans 12º. These bands are referenced by letter from South to North,
beginning with the letter C at 80ºS and running to letter X at 84ºN, with I and O omitted. Polar
areas are covered by a different system that we will not discuss in this lab. Each block created
by the intersection of the horizontal bands with the UTM zones can be referenced by number
and letter, specifying a general area. Southeastern Arizona, for example, includes 12S and 11S.
Figure 10. UTM zones in the continental United States
Within each block, locations are identified using two coordinates, a "northing" value and an
"easting" value. In the Northern Hemisphere, the northing is measured in meters from the
equator; for example, a northing of 500,000 means a location is 500,000m (500 km) north of the
equator. The easting is measured differently. Within each zone, a central meridian is run down
the middle and assigned an arbitrary value of 500,000m. Locations to the west have easting
values lower than 500,000 while locations to the east have higher values.
LAB QUESTIONS
Answer the following questions, using the topographic map of Harrisburg, Pennsylvania.
SECTION A: Magnetic declination
1. What is the magnetic declination of this map? _______________
2. Since this declination was measured in 1956, do you think this value is still accurate? Explain.
SECTION B: Compass directions
1. What is the general orientation of the mountain ridges shown on the map? ______ to ______
2. What is the name of the city found closest to the southeast corner of the map? ___________
3. The city of Enola is located on which bank of the river Susquehanna? __________________
SECTION C: UTM coordinates
In this section, you need to use UTM coordinates to find the locations indicated in each question
below before you can answer the question.
1. Would you say the slope located at 4478000m N and 351000m E is steep or gentle? Explain.
2 What physical feature is found at 4480000m N and 340000m E? _______________________
3 If you were to walk from 4475000m N to 4473000m N along the line 351000m E, would you
be walking upslope or downslope? _____________________________________________
4. The contour interval of this map being 20ft, what is the elevation of the summit of the
mountain located at 4467800m N and 333000m E? ___________________________________
SECTION D: Refer to the legend provided at the end of this lab to answer the following
questions.
1. Is the Blue Mountain ridge forested or not? Explain.
2. What type of stream is Stony Creek? ____________________________________________
3. Is there a racetrack in Harrisburg? ______________________________________________
4. What type of road passes on Taylor Bridge? ______________________________________
SECTION E: Scale and distance
1. Calculate the distance in miles between the NW corner and the SE corner of the map.
2. Two inches measured on the map with a ruler would equal how many miles in ground
distance.
SECTION F: Using topozone.com to find topographic maps
Using Netscape Navigator, Microsoft Internet Explorer, or some other web browser of your
choice, navigate to Topozone.com’s homepage: http://topozone.com/. If you have problems
getting to this web page, try a few times to see if it’s just busy. Once you are at the page you
should see a small picture of the day’s featured map.
N.B. The site is sometimes down; so do not wait until the last minute before your lab to answer these
questions. No extra time will be allowed for this part of the lab to be completed.
To find a specific map, type in the name of the place you are interested in using the “Place
Name Search” shown in green lettering along the left side of the screen, below the featured
map. Place your cursor in the white box, click, and type in the name of the place you are
interested in finding. The map you have to use is that of Marana, AZ. So, type “Marana” in the
white box and then, using the drop down list of states to the right, choose AZ. Then, click on the
gray box that says Search.
This will bring you to a page that shows a table containing all the maps available for the location
you typed in. In this case, you will have two maps. For this exercise, use the information for the
“town/city” listing, rather than the “locale” listing.
1. What county is Marana located in?
2. What is its elevation?
3. What is the name of the USGS Quadrangle (Quad) that has Marana on it?
4. Determine the length of the portion of the Santa Cruz River that is displayed on this
map (measure the distance directly on the computer screen).
SECTION G: Analyzing Marana’s topographic map
Now, click on the hyperlink for Marana “town/city”.
The map will be displayed at the representative fractional scale of 1:50,000 and a small map
size. Change the RF scale to 1:100,000 and the map size to large by using the drop down menu
that says “1:50,000” under the “View Scale” heading, and clicking on the “Large” button for the
map size. Do not forget to click the “Update Map” button to update your map.
You will notice several green triangles around the sides of the map itself. Clicking on these
arrows will show you the maps that are adjacent to the one you are viewing. Also, left clicking a
spot on the map itself will center the map to that location.
To zoom on selected features of the map, just click on the location and use a larger scale.
1. What is the magnetic declination for this map?
2. Give the general compass orientation of the Santa Cruz River from the upper left
corner to the lower right corner of the map.
3. Find the following features on the map and use the legend found at the end of this lab
to determine what they are.
a) The small black squares.
b) The areas of irregular green “dots” to the north and south of the Santa Cruz River.
c) The brown irregularly spaced dots within the banks of the Santa Cruz River.
d) Note on the legend that rivers are usually shown in blue. Why is the Santa Cruz
represented with brown symbols instead?
f) Find the dark brown area near the bottom right corner of the map. Click on this feature
to re-center the map to that location. Then, zoom back in to 1:50,000 so that you can see
this feature up close. What is this feature?
g) What is the approximate elevation of the Northeast corner of this feature?
N.B. Remember that specific elevations are shown as black numbers
h) Notice that several of the contour lines associated with this feature have hatch marks.
What does this mean?
i) The contours around this feature are 2010, 2020 and 2030. Given these values, what is
the contour interval?
PARTIAL TOPOGRAPHIC MAP LEGEND