1. EarthReading3: Topographic Map Primer
THE SUNNYSLOPE QUADRANGLE, ARIZONA

2. Introduction:
Topographic Maps are important tools of the Earth scientist. Many features are shown on the map by the use of CONTOUR lines. A contour line is a line that connects points of equal elevation. The starting point (0 foot contour line) is sea level. On the topographic map these lines are shown as brown lines (*) When this symbol (*) appears in the text it is your cue to press the enter key or space bar to advance to the next image.)
I have a video that will walk you through the basics of contour in nine minutes. Then, come back to this presentation and go on to the next slide. Click here.

3. Introduction: Contour Lines:
In general, note how the contour lines are sub – parallel, they never cross or touch and they never split.
Notice also that every 5th line is a heavier line. These are called index contour lines and they are emphasized on the map to make the counting of contour lines easier.
For example the index contour directly above the 2000 line is (*)
How can you tell? You have to find out what the contour interval is. This bit of important information is located at the bottom center of the map. (*)

4. Introduction: Contour Lines:
Below it also states: Dotted lines represent 10-foot contours. (Below that it states that the data for the contour lines was bases on information obtained in 1929.)(*)
Here is an image of the bottom of the map. There is a lot of information located here, but for now take a look at the area below the graphical scales. (*)
Below the scales it says the contour interval is 20 feet. (*)

5. Introduction: Contour Lines:
In this part of the map there is a contour of (*)
The next “normal” contour line would be the 1160 which is 20 feet higher. Find it on the map.(*)
But, this area of the map is so flat that another contour line was added. Instead of the normal 20 feet on the map it is only 10 feet different than the one above or below it. (*)
This is not the normal situation on topographic maps. (*)

6. Introduction: Contour Lines:
So, you can see that the difference in elevation from one normal contour line to the next is 20 feet. The dotted contour line is found only in the flat area of the map. (*)

7. Introduction: Contour Lines:
Back to Squaw Peak – Now that you understand that the normal contour lines are separated 20 feet from the lines above it and below it, it makes sense that every 5th line is 100 feet difference in elevation. To make it easier to count these lines the 5th line is darkened. These are the INDEX COUNTOUR lines. (*)
Check out the position of the 1700 foot line. (*)
What is the elevation of the little unnamed hill just above it on the right side of this illustration? (*)

8. Introduction: Contour Lines:
What is the elevation of the little unnamed hill just above it? Remember the purple line is the 1700 foot line. (*)
Going up to the summit (blue dot) of the hill, the next INDEX CONTOUR line is the 1800 foot line (red line). (*)
Finally, there is one more index contour line closer to the summit. This is the foot contour line (black) (*)
1900
BUT, we are not yet quite to the summit. There are 3 normal contour lines. The next contour line would be the 1920, the next is the 1940 and the one closest to the summit is the (*)
Summit
So, the summit of this hill is a little over 1960 feet. But it is below 1980 – otherwise there would be another contour line. (*)

9. Introduction: Contour Lines:
While your looking at Squaw Peak, notice that the brown contour lines have different spacing. Where the contour lines are close together, there is a steeper slope. Where the contour lines are farther apart, the slope is more gentle. (*)

10. Introduction: Contour Lines:
One last thing about contour lines is that they “V” upstream when they cross a river drainage. Check out one of the many unnamed streams on the map below. Blue represents water features on topographic maps, and the line and three dot pattern of the streams on this map indicate an intermittent stream – sometimes it flows and sometimes it doesn’t. (*)
Next, notice how the contour lines form a “V” and that the “V” points towards the top of Squaw Peak (higher elevation), The rule of thumb is that the “V’s” point upstream,(*)
There are even other drainages that are not marked by streams but simply by the pattern of the “V”s. (*)

11. In this illustration of North Mountain Park (top central area of map) all the stream drainages will be highlighted in purple. It includes the blue stream lines as well as the unmarked drainage. Before you advance to the next image see if you can visualize where this additional drainage would be on just the west side of the mountain. (*)
What was done was to draw a line that connects the tips of the “V”s. As you can see, this is a good example of dendritic (branching) drainage. (*)

12. Let’s take another look at the information at the bottom of the map. (
This is the name of the map and when it was created.
Photorevised means that the map was reevaluated in 1982 and that changes to the 1965 map were indicated in purple. Obviously, the map needs to be revised again. (*)

13. Let’s take a look at the scale next. (*)
Let’s take another look at the information at the bottom of the map. (*)
This is the location of the Sunnyslope Quadrangle with respect to the rest of the state of Arizona.

14. The top scale is called the fractional scale: Scale 1: 24000. (*)
This simply means that an inch on the map is equivalent to inches on the surface of the Earth. OR 1mm on the map is equivalent to mm on the Earth’s surface. (*)
The top scale is called the fractional scale:
Scale 1: (*)
One unit of ANYTHING on the map is equal to of those things on the Earth Surface. (*)
Let’s take another look at the information at the bottom of the map. (*)
This is the area of the two scales. (*)

15. This is the graphical scale
This is the graphical scale. The one you will be using in the lab is the mile scale (the top of the three scales). Note that the total length of the scale is 2 miles. (*)
Let’s take another look at the information at the bottom of the map. (*)
The left side of the scale is divided into 1/10’s and the right side is one mile. It is very important to note the zero in the middle. It could make a huge difference in your measurements and thus the accuracy of your answers. (*)

16. Some Basic Information about Topographic Maps
COLORS:
BLACK – Artificial features like buildings, dams, trails, railroad lines
BLUE – Water bodies or glaciers
BROWN – Contour lines
GREEN – Vegetation
RED – Some main roads, fences, public land system revisions
PINK – Urban areas
PURPLE - Revisions
(*)

17. DETERMINING POSITION ON THE MAP
TWO BASIC TECHNIQUES
The Public Land Survey (PLS)
The Public Land Survey system is a grid system based on points of reference across the United States. All reference sites are located with reference to a BASELINE which is an east – west line and a MERIDIAN which is a north – south line. (*)

18. From this point an east – west line is drawn. This is the BASELINE.
The Public Land Survey (PLS)
From this point an east – west line is drawn. This is the BASELINE.
BASELINE
This dot represents a spot of geographic prominence in an area. It could be a hilltop, the confluence of two rivers or any easily recognizable and easily accessible point. (*)
Next a north – south line is drawn. This is the MERIDIAN.
MERIDIAN
The next step in the survey is to accurately establish more north – south and east – west lines at 6 mile intervals. (*)

19. The Public Land Survey (PLS)
These vertical north – south lines can also be extended farther east or west by the survey team. (*)
6 miles
6 miles
6 miles
6 miles
6 miles
BASELINE
6 miles
6 miles
6 miles
6 miles
MERIDIAN
6 miles
6 miles
These east – west line can extend as far as needed by the survey team. (*)

20. The Public Land Survey (PLS)
From this basic grid pattern a system of location can be established.
Where is the star located? (*)
BASELINE
MERIDIAN
It is located on the second row south of the BASELINE and on the fourth column to the west of the MERIDIAN. (*)

21. The Public Land Survey (PLS)
This is basically how it is done, except that the rows – the horizontal squares are called TOWNSHIPS and the vertical squares are called RANGES. (*)
BASELINE
Range 4 West
Range 3 West
Range 2 West
Range 1 West
Range 1 East
Range 2 East
Range 3 East
Range 4 East
The Townships are numbered in a similar manner. (*)
MERIDIAN

22. The Public Land Survey (PLS)
This is basically how it is done, except that the rows – the horizontal squares are called TOWNSHIPS and the vertical squares are called RANGES. (*)
Range 1 East
Range 2 East
Range 3 East
Range 4 East
Range 1 West
Range 2 West
Range 3 West
Range 4 West
Township 4 North
Township 3 North
Township 2 North
BASELINE
Township 1 North
Township 1 South
Township 2 South
Township 3 South
MERIDIAN
Township 4 South
So the star is located in Township 2 South and Range 4 West. T2N. R4W (*)

23. That star is in a square that is 6 miles on a side
That star is in a square that is 6 miles on a side. This is an area of 36 square miles. If that star were your house and you told a friend that it was located in Township 2 South (T2S) and Range 4 West (R4W), your friend may have a hard time finding your house. (*)
So each of these 36 square mile areas (these are called townships) is divided up into 36 squares. Each square is 1 mile on a side or 1 square mile in area. (*)

24. Each square of the township is called a SECTION
Each square of the township is called a SECTION. There are 36 sections in a township. Note how they are numbered - (*)
Now you can narrow down the area of where the star is located. It is located in Section 29 of T2S and R4W. (*) 6 5 4 3 2 1 7 8 9 10 11 12 18 17 16 15 14 13 19 20 21 22 23 24 30 29 28 27 26 25 31 32 33 34 35 36

25. So the star is located in the NE quarter of Section 29, T2S, R4W.
One square mile (a section) is a very large amount of land. Again, if it were your house and you told someone that you lived between Olive Ave and Peoria and Between 51st Ave and 59th Ave, they would find your house, but it would take a while. The area mentioned is actually one square mile. (*)
To make it easier, the section is further divided. It is divided into quarters.
The star is located in the top right quarter of the section. In PLS terminology the star is in the northeast quarter of section 29. Here are the quarter designations. Remember that north is always to the top. (*)
NW 1/4
NE 1/4 29
SW 1/4
SE 1/4
So the star is located in the NE quarter of Section 29, T2S, R4W.
In most cases this may be enough to locate an object on a topographic map. But each of these quarter can be subdivided into quarters. (*)

26. Each of the ¼ of a square mile can be further divided into quarters. (
The top right quarter becomes the NE ¼ of the NE ¼. Followed by the NW, SW and the SE ¼’s.
NE 1/4
NW 1/4
SW 1/4
SE 1/4 NW NE SW SE 29
So the star is located in the NE ¼ of the NE 1/4 of Section 29, T2S, R4W.
This will be the extent of using the PLS system in the lab. But you can see that even this little (¼ x ¼ = 1/16 of a square mile) NE ¼ can further be divided into many more quarters to create a smaller area in which the object is located. This is the method of location commonly used by real estate as well as many cities and municipalities. (*)

27. The second method of location is by latitude and longitude
The second method of location is by latitude and longitude. With the extensive use of GPS – Global Positioning Satellites, latitude and longitude is the preferred method of location of an object anywhere on the surface of the Earth. Current technology allows a common hand-held GPS unit to determine position to within an accuracy of about 1 inch (although the US military has degraded the signal for security reasons so that the hand-held units are accurate to only within 10 feet. (*)
Actually there are a total of 24 satellites that are in the “constellation” that orbit the Earth. (*)
Earth

28. Latitude and Longitude
The spherical Earth is divided into a grid pattern using north-south lines (longitude) and east-west lines (latitude). The basic east west line is the Equator This is the zero line of latitude. Parallel lines above and below the equator are then drawn in. The poles are 90o north and south of the equator. (*)
The basic north-south line is called the Prime Meridian, it is the zero line of longitude. It is drawn from the geographic north pole to the geographic south pole through Greenwich, England. Then other north south lines are drawn in east and west of the prime meridian. (*)
Using this grid, any point on the Earth’s surface can be given an east-west and north-south designation. (*)

29. Angular measure refers to distances along a sphere. (*)
As an example we will take a look at a portion of the Sunnyslope map – the top right hand corner of the map. (*)
This RED line is a line of latitude. It represents an angular measure that is 33o 37’ 30” above the equator. This reads: 33 degrees (o), 37 minutes (‘) 30 seconds (“). (*)
33o 37’ 30”
To Equator
Angular measure refers to distances along a sphere. (*)

30. ANGULAR MEASURE IN LATITUDE AND LONGITUDE
North Pole
This is a cross sectional view of the Earth with the white dot being the center of the Earth. (*)
Equator
This line drawn from the center out to the Earth’s surface is drawn at 30o above the equator. (*)
30o
So, if you were standing on the spot where this line emerged from the center of the Earth you would be 30o above the equator. (*)

31. ANGULAR MEASURE IN LATITUDE AND LONGITUDE
Equator
In a similar way, if you are looking down on the Earth’s North Pole (now the white dot) the prime meridian is the bold red line passing through Greenwich, England.
Prime Meridian
This line drawn from the center out to the Earth’s surface is drawn at 30o east of the prime meridian. (*)
30o
So, if you were standing on the spot where this line emerged from the center of the Earth you would be 30o east of the prime meridian. (*)
Take a look at the map again. (*)

32. One other note about angular measure, one degree is divided into 60 minutes and each minute is divided into 60 seconds. If you think of a degree as being an hour, then it makes some sense. (*)
1o = 60’
1’ = 60”
Take a closer look.
This small part of a circle is one degree. It can be divided into 60 equal parts. Each part is 1 minute (1’). (*)

33. This view shows the one degree segment enlarged on the right
This view shows the one degree segment enlarged on the right. It is divided into 60 equal parts. Each one of these parts is a minute. (*)
1o = 60’
1’ = 60”

34. This view shows the one degree segment enlarged on the right
This view shows the one degree segment enlarged on the right. It is divided into 60 equal parts. Each one of these parts is a minute. (*)
1o = 60’
1’ = 60”
Each tiny minute is further subdivided into seconds. There are 60 seconds to every minute.
It is obvious that 1” is a very small angular measure.
Back to the map. (*)

35. Focusing in on the top right hand corner of the map, note the 112o 00’ mark. This is 112o and 00’ west of Greenwich, England. This is longitude. (*)
The latitude is 33o 37’ 30”. The top right hand corner of the map is thirty three degrees, thirty seven minutes, thirty seconds above the equator. (*)
To England
112o 00’
33o 37’ 30”
To Equator

36. Notice that the difference in longitude is 7’ 30’.
One last look at latitude and longitude. Here are the corners of the map. (*)
Notice that the difference in longitude is 7’ 30’.
Notice also that the difference in latitude is 7’ 30”.
That is why this map is called a 7.5 minute series map.
It is 7 ½’ in latitude by 7 ½’ in longitude.
The last part of this Power Point deals with GRADIENT. (*)

37. This is the stream that will be used as an example.
Stream Gradient
Stream gradient is the slope of the stream. Like the slope of a line in algebra which is the rise/run, the slope of a stream is the difference in vertical elevation (rise) divided by the horizontal distance (run). (*)
Find this area on your topographic map. (*)
This is the stream that will be used as an example.

38. The difference in elevation (rise) is 620 feet. (*)
Stream Gradient
In this example we will use the beginning of the stream as the starting point and where the stream enters into the purple revisions area as the ending point.
The vertical displacement of the stream (rise) is simply the difference in elevation from where it starts to the end of the profile. (*)
The elevation here is 2020 feet. It is one contour line above the 2000 foot index contour. (*)
The elevation of the end point is right on the 1400 foot index contour line. (*)
The difference in elevation (rise) is 620 feet. (*)

39. Stream Gradient
The horizontal difference (run) is determined by taking a string and laying it on stream. As you lay it on the map be sure to match as closely as possible the curves of the stream. (*)
Next, take the string down to the graphical scale on the bottom of the map and measure its length in miles to the nearest 1/10. (*)

40. To determine the gradient you simply divide the rise by the run. (*)
Stream Gradient
I measured the stream using the string a found that it was about 0.5 miles on the scale. (*)
To determine the gradient you simply divide the rise by the run. (*)

41. Stream Gradient GRADIENT = ADD THE NUMBERS NEXT (*)
DIFFERENCE IN ELEVATION (ft)
GRADIENT =
Divided by
HORIZONTAL LENGTH OF STREAM (miles)
ADD THE NUMBERS NEXT (*)

42. Stream Gradient GRADIENT = = 1240 feet/mile (*) 620 feet (rise)
0.5 miles (run)
On the quiz and on the test I will allow for some error in your measurements. (*)

43. This concludes this Power Point
Although it was somewhat long, it was complete and reiterated (repeated and reinforced) ideas and skills from earlier in the class. I wanted to be sure that I covered all the various aspects of the basic applications of topographic maps and, of course, all the kinds of questions that I will be asking on the assessments. Feel free to me if you have any questions.
After finishing this power point, you will complete EarthLab3 in class.