Lab 5 Topographic Maps_FA21
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Apr 3, 2024
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Laboratory Exercise 5: Introduction to Topographic Maps
Introduction to Geology II: Earth’s Surface Processes
Name: Keyli Alvarado Score: ___/25
INTRODUCTION
The primary purpose of this lab is to practice some basic map and math skills that we will be using in this course. We will use latitude and longitude to determine location, map scales to calculate distance, contour lines to determine elevation, and both scales and contours to calculate the change in elevation over a distance (slope). You may find it useful to review the videos and websites in the Lab Tutorial section of this week’s module. You should fill in your answers directly on this document, save and upload it to Canvas. Please save it as a .doc or .docx file, and use your last name and name of the lab in its saved file name (example: Stoklosa_Lab 5.docx).
Part A: Finding Locations on Maps Every location on a two-dimensional surface (like a topographic map) can be specified by 2 pieces of information. In math, you use x and y coordinates, on a road map you use a letter and a number to find the location on a map grid. To describe locations on the surface of the Earth, we use a grid formed by lines of latitude and longitude.
Lines of latitude are circles in the east-west direction
that go around the Poles. The largest circle in the
“middle” of the globe is the Equator. It separates the
northern hemisphere from the southern hemisphere.
The Equator has the latitude of 0
o
, the North Pole has
90
o
N, and the South Pole has a latitude of 90
o
S. (The
symbol o
is called a “degree.”) In the example to the
right, the dot labeled “A” is on the 30
o
N line, so its
latitude is 30
o
N. Some of the locations that you will be
asked to find are not on a line with a number, so you
will need to estimate the latitude. The dot “B” is about
mid-way between 30
o
N and 60
o
N, so its latitude is
about 45
o
N. Notice that lines of latitude run east-west,
but they determine position north or south of the
Equator. Every location along a line of latitude is the
same distance from the Equator, so they all have the
same latitude.
© Michelle Stoklosa 2020
1
Lines of longitude are half-circles
that run from the North Pole
to the South Pole. The 0
o
line of longitude (called the “Prime
Meridian”) runs through Greenwich, England, and divides the
eastern hemisphere from the western hemisphere. Dot “C” in
the picture on the right has a longitude of 30
o
E, while dot “D”
has a longitude of about 15
o
W. Halfway around the world,
the 180
o
line of longitude divides the eastern and western
hemispheres, but ironically, the eastern hemisphere is on the
western side of the line and vice versa! Notice that lines of
longitude run north-south, but they determine position east or
west of the Prime Meridian.
For finding specific locations, degrees of latitude and longitude are far too large to be useful. To make them more precise, a degree of latitude or longitude is divided into 60 smaller parts called “minutes.” The symbol for minutes is an ‘
(like an apostrophe), so 1
o
= 60’. The latitude of dot “E” (in the picture to the left) is 22.5
o
N, which is 22
o
30’N (22 degrees
30 minutes north of the Equator). In other words, half a degree is 30 minutes, just as half an hour is 30 minutes. The
dot “E” is about a quarter of the way between the 77
o
W and 78
o
W lines of longitude, so it has a longitude of 77
o
15’W. A quarter of a degree is 15 minutes, just as a quarter of an hour
is 15 minutes.
As you have probably already guessed, sometimes minutes are not precise enough for finding locations. Therefore, minutes of latitude and longitude are divided even further into 60 smaller parts called “seconds.” The symbol for seconds is ” (like quote marks), so 1’ = 60” (one minute is equal to 60 seconds).
If you haven’t already done so, review the “Latitude and Longitude”
video in this week’s video tutorials for the lab exercise before completing Task A1.
Task A1: Determining latitude and longitude on a map Using the map on the next page
, determine the latitude and longitude of the following places. Answer to the nearest degree
-- round up and don’t use minutes or seconds. For example, answer 34
o
N instead of 33.5
o
N or 33
o
30’N. Don’t forget to include N, E, S, or W. (7 points)
© Michelle Stoklosa 2020
2
Place
Latitude
Longitude
New Orleans, Louisiana
30 N
90 W
Galapagos Islands, Ecuador
0
90 W Sao Paolo, Brazil
29 S
50 W
Alexandria, Egypt
30 N
40 E
Shanghai, China
30 N
120 E
Sydney, Australia
35 S
140 E
Greenwich, England
55 N
0
Task A2: Finding locations on a map
Put a bold or red X at each of the locations of the following latitudes and longitudes on the map
above. (2 points)
Great Barrier Reef
18
o
S, 147
o
E
Mt. Everest
28
o
N, 87
o
E
Portland, Oregon
45
o
N, 122
o
W
Tahiti
18
o
S, 150
o
W
Note: If you can’t figure out how to add an x to this image, you might print out this page, draw in each x, and then take a photo. You will then need to upload this photo with the rest of your assignment, or embed it into your document.
© Michelle Stoklosa 2020
3
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Task A3: Determining latitude and longitude on a map of Vancouver (2 points)
Download the Vancouver Topographic Map from this week’s module. You will need to have Adobe Acrobat Reader in order to view this map and have some patience while it downloads. Don’t just view it within Canvas…actually click on “Download Vancouver Topographic Map”. Once it opens, make sure that the Image layer is turned off; it requires a lot of memory to view and interferes with viewing the contour lines on these maps. Zoom in by selecting 100% in the
menu at the top, and look around. Note the latitude and longitude notations at the corners of the map. Make sure you know which numbers are the latitude and which are the longitude (use the posted videos or other sources to check, or ask for help).
1.
How many minutes of latitude are represented on this map? (Subtract one latitude value
from the other…these are at the top and bottom) 7.5 minutes. 2.
How many minutes of longitude are represented on this map? (Subtract the differences in longitude; these are found on the left and right corners 7.5 minutes 3.
This type of map is referred to as a “Seven-and-a-half-minute quadrangle”. Explain why.
Because is named after the most prominent feature in the quadrangle. Part B: The Meaning of Map Scales “Fractional” maps scales are ratios. In other words, they take the form 1:2, 1:20, 1:100, 1:3,000, 1:24,000 and so on. The scale tells you about the relationship between the map and the real world that it represents. For example, everything in a map with a scale of 1:10 is 10 times smaller than in the real world (or you could say that the real world is 10 times larger than what is shown on the map). You can use the scale to measure distances on a map. If a map has a scale of 1:5000, then 1 inch
on the map represents 5,000 inches
in the real world (or 1 centimeter on the map represents 5,000 centimeters in the real world or 1 foot on the map represents 5,000 feet in the real world). The units that you use do not matter, as they are the same on each side of the colon when using a ratio.
If you haven’t already done so, review the “Map and Compass Basics” video
in this week’s video tutorials for the lab exercise before completing this part of the exercise.
Task B1: Reviewing fractional scales (1 point)
A map has a fractional scale of 1:100,000
1.
One inch on this map represents how many inches in the real world? ______100000 in ______ 2.
How many miles does this one inch represent? (Show your work below) _1.578___________
© Michelle Stoklosa 2020
4
Task B2: Fractional Scale of the Vancouver Topographic Map (3 points)
Look again at the topographic map of the Vancouver area that you used in part A. Look around the bottom of the map for the fractional scale.
1.
What is the fractional scale
of the Vancouver Quadrangle? (You should increase the viewing scale on the map to 100% in order to scroll around and find this information).
1:24000
2.
How many feet (in the real world) does one inch on this Vancouver map represent?
(Reminder: 12 inches are in one foot. Show your work below.)
2000ft 3.
Suppose that you are looking for a map, and you are told that you can choose between maps with several different scales: 1:1,000, 1:50,000, 1:100,000, or 1:500,000. Which map would show the most
detail?
1:1000
Part C: Reading Elevation from Contour Maps, Relief and Gradient At first, a contour map may appear to be a bunch of squiggly lines. The squiggly lines are contour lines (or simply contours). A contour line connects locations that are at the same elevation. In the contour map below, the location labeled “A” has at an elevation of 10 meters, because it is on the 10-meter contour line. The location labeled “B” has an elevation of 20 meters. If a location is between contour lines, then use the neighboring contour lines to describe its value. Location “C” is between the 10- and 15-meter contour lines, so it is between 10-15 meters in elevation. Location “D” is between 15-20 meters in elevation. Don’t make up an elevation…just tell me what you know, even if it is just a range.
© Michelle Stoklosa 2020
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Unfortunately, not every contour line is labeled, typically because they get too close together. In this case, you must figure out the value of each contour line using the “contour interval.” The contour interval is the difference or “jump” in value from one contour line to its neighboring
contour lines. In the contour map above, the contour interval is 5 meters, because the difference between each contour is never more than 5 meters. Therefore, the blank contour line with location “E” on it must have an elevation of 25 meters (mid-way between 20 meters and 30 meters, the values of neighboring contour lines). Notice that neighboring contour lines can have the same value. For example, two 20-meter contour lines are next to one another in the map above. Contour lines can never touch one another (“cross”) or divide (“split”). If the contour lines loop around
and connect with themselves, then the location is a hill or basin.
If you haven’t already done so, review “Introduction to Topographic Maps” video
in the video tutorials for this week’s lab. Task C1. Using a topographic map to estimate elevation (2 points)
Use the image of the map on the previous page to address the following questions.
1.
In the map above, what is the elevation of F? [Remember to always include units.] 25 meters © Michelle Stoklosa 2020
6
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2.
In the graphic above, what is the elevation of point G? [Give a range, and remember to include units.] Task C2: Using contour lines to calculate gradient
Notice on this map and graphic that there are thin and thick contour lines. The elevation between any two adjacent contour lines of different elevation on a topographic map is the contour interval, which will be listed on the bottom of the map. The contour interval for this map is 20 feet. Often every fifth contour line is thicker. These heavier contour lines are known
as index contours
, because they generally have elevations printed on them. The index contours for this map are 100 feet. Index contours are your starting point when reading elevations on the topographic map.
There are two additional concepts we will use in this course. Relief is the difference in elevation between landforms, specific points, or other features on a landscape or map
. You can calculate relief using the following formula:
Relief
=
High Point
−
Low Point
Gradient is a measure of the steepness of a slope
. On a topographic map, gradient is usually determined by dividing the relief (rise or fall) between two points on the map by the distance (run) between them. In mapping, the gradient is generally expressed as a fraction in feet per mile or meters per kilometer. It represents the change in elevation over a distance.
Gradient
=
Relief betweentwo points
(
thedifference
∈
elevationbetweentwo points
)
Distance betweenthe two points
You may be familiar with the
way gradient is often referred
to, as “rise over run.”
Gradient
=
Rise
Run
Use the Vancouver
Quadrangle to address the
following questions: (5
points)
© Michelle Stoklosa 2020
7
1.
What is the contour interval in feet
? ________
2.
What is the regional
relief of this map
? Do your best to find the highest and lowest elevation points on the entire map, then subtract to get the answer.
Show your work below and include units.
3.
What is the
approximate elevation of the downtown Vancouver post office? (Hint: look for the red F…between which two contour lines is it located? Give that range rather than estimate. Don’t forget to include units!)
4.
Now calculate the gradient
between the Columbia River (starting at the shoreline right by the Port of Vancouver Terminal) and Saint James Cemetery. To figure out the elevation of these two points you will need to use the contour lines (and subtract the difference between them). To figure out the distance between these points, you might either print out the map and measure, or measure using a piece of paper held up to the screen. For this example, be sure to use the graphical scale (not the fractional scale),
to calculate the actual distance. The graphical scale can be found below the fractional scale, like on the example below:
Show your work below
, and give your gradient in feet/mile
. Part D: Topographic Profiles
© Michelle Stoklosa 2020
8
It is easier to visualize the ruggedness of a terrain shown on a map by drawing a topographic profile. Remember the elevation profile that you made in Google Earth for the Week 3 lab? This is the same thing, and we will continue to use these profiles throughout the term. This week we will learn how to create them using a topgraphic map, rather than Google Earth. Review the video “Creating Topographic Profiles” and “Making Topographic Profiles using Power Point or Google Slides” in the video tutorials for the lab in this week’s module in Canvas.
Task D1: Creating a topographic profile (3 points)
Draw a topographic profile from A to A’ on the graph below the map on the next page. Label the units on the x- and y-axis
. Note: these profiles are best done by hand so if you have a printer, print the file titled “Grid and Map for Week 5 Profile.jpg” that is found in the Week 5 (week 4 of the term) module. Take a picture of it and submit it along with the rest of your lab. If you do not have a printer, follow the instructions in the “Making Topographic Profiles using Power Point or Google Slides” video in Canvas and submit the file along with your lab. © Michelle Stoklosa 2020
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Congratulations! You are now familiar with how to use a topographic map! We will continue working on some basic aspects of topographic maps in a few weeks, and will continue to use them throughout the term. If you would like to find other topographic maps, go to the National Map Viewer site, from the USGS (United States Geological Survey): https://viewer.nationalmap.gov/advanced-viewer/
and start searching!
© Michelle Stoklosa 2020
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