A map is a graphic representation of a portion of the earth's surface as seen from above, drawn to scale. A map provides information on the existence, the location of, and the distance between ground features such as towns and roads. Whenever possible maps should be protected by lamination, and care must be taken so that they may last as long as possible. There are several different types of maps. The following is a list of the types of maps that you will most commonly use.

Topographic maps: This is your typical USGS map. It portrays variations in terrain, heights of natural features, and the extent of vegetation cover. Relief is normally represented by contour lines. Each topographic map is commonly referred to as a 'map sheet.'
Terrain models: This is a scale model of natural and man-made terrain features. It provides a means to visualize the terrain depicted on a map in three dimensions.
Photo and Photomosaic maps: This is a reproduction of an aerial photograph or a series of photographs, upon which grid lines, marginal data, place names, route numbers, important elevations, boundaries, and approximate scale and direction have been added.

II. What Does A Topographic Map Show?

Topographic maps not only depict a portion of the earth's surface to scale, but also incorporate marginal information to assist the map user.

A. The Marginal Information on a USGS Topographic Map

Note: Depending on the age of the topographic map being used, the marginal information may vary. The following list details that marginal information that is currently standard to all USGS topographic maps.

Map Producer Identification: The agency which produced the map is identified in the top left-hand corner of the map sheet.

Map Sheet Name: The sheet name is found in two places; the top right-hand corner and the lower right-hand corner of the map sheet. A map sheet is named after the most prominent man-made or natural physical feature depicted on that sheet. Also found here is the area of the earth's surface portrayed on the map. For example, if a map sheet is a 7.5 minute series or quadrangle, then it covers 7.5 minutes of latitude and longitude. This can also be determined by observing the latitude and longitude coordinates of the four corners of the map.

Map Specific Legend: This legend depicts features specific to this map sheet is located in the lower right-hand corner.

The State Locator: Graphically depicts the location of the map in respect to a state's boundaries, and can be found in the lower right-hand side of the map.

Scale: The scale of the map is found in the bottom center of a map sheet. The scale gives the ratio of map distance to the corresponding distance on the earth's surface.

Graphic Bar Scales: Are found at the bottom center of the map sheet. These are rulers used to convert map distances to ground distances, and to convert distances between different units of measure.

Contour Interval: Is found at the bottom center of the map sheet below the graphic bar scales and shows the vertical distance between contour lines on the map and the unit of measure used.

Declination Diagram: (Sometimes referred to as the G-M, grid-magnetic, angle) Is found in the lower margin of the map sheet to the left of the graphic bar scales. The declination diagram is the angular difference between true north and either magnetic or grid north, for the particular portion of the earth's surface depicted on the map. Declination diagrams are seldom plotted exactly to scale. The relative position of the directions is obtained from the diagram, but the numerical value of the declination should never be measured from the angles. Use the written value of the declination provided to the left and right of the diagram.

Datum Information: Is found below the contour interval note. It contains information that can be used with a GPS unit.

Map Information Note: Contains information about the production of the map and can be found in the lower left-hand corner of the map sheet

Index to adjoining sheets diagram: Is found in the lower right-hand portion of the map sheet and depicts the location of the map sheet you are using in respect to the adjoining sheets. On older USGS maps, the names of the adjoining quadrangles are labeled along the four sides of the map.

B. Topographic Map Symbols

The modern system of map symbols owes much to the reign of Napoleon Bonaparte. During the first part of the 19th century France became the leader in cartography whith the introduction of such cartographic inovations as a compreshensive system of incorporating symbols onto topographic maps. Many of the standard symbols used on USGS topographic maps are listed below.

C. Colors used on Topographic Maps

On a standard topographic map, the colors used and the features they represent are:

Black: Indicates man-made features, such as buildings.

Gray: Indicates built-up areas, relief features, and elevation. This color enables the map to be red-light readable. Note: on older topographic maps, built up areas are indicated by red.

Red: Is used to depict major roads and highways.

Brown: Is used to depict contour lines.

Green: Identifies vegetation, such as woods, orchards, and vineyards.

Blue: Identifies water features, such as lakes, swamps, rivers, and streams. Intermittent water features are depicted with a dashed line.

III. How Is a Topographic Map Used?

A. Determining Locations: Locations of features depicted on a topographic map can be determined by using latitude and longitude (also known as the geographic coordinate system), township and range land survey system, or the military grid reference system (MGRS).

1. Latitude and Longitude: In a previous module you already learned about one of the oldest systems for determining location, latitude and longitude which is based upon the geographic coordinate system. For review, it is composed of parallel imaginary lines encompassing the globe. The lines that run east and west are called lines of latitude, and the lines that run north and south are called lines of longitude. Today, this reference system is used primarily for air and naval navigation.

Latitude: Midway between the North and South Poles is an imaginary line that runs east and west around the surface of the earth. It is called the equator. The equator is the starting point (zero) for all measurements of latitude. Parallel to the equator are other imaginary evenly spaced lines. Starting at the equator, these lines of latitude are numbered from 0 to 90 both to the north and to the south, and are labeled in degrees. Because lines of latitude can have the same numerical value north and south of the equator, the direction must be specified. 90 degrees north latitude is known as the geographic north pole, and 90 degrees south latitude is known as the geographic south pole.

Longitude: An imaginary line runs north and south through Greenwich, UK. It is called the prime meridian and is the starting point (zero) for all measurements of longitude. Starting at the prime meridian these lines of longitude are numbered from 0 to 180 both to the east and to the west, and are labeled in degrees. Because lines of longitude can have the same numerical value east and west of the prime meridian the direction must be specified. 180 degrees east and west longitude is known as the international date line. Note: Not all countries recognize the prime meridian that runs through Greenwich. A note will usually be added to the marginal information of a map if this is the case.

Measurements for the geographic coordinate system are expressed in degrees, minutes, and seconds. There are 60 seconds in a minute ( " ), 60 minutes in a degree ( ' ), and 360 degrees in a circle ( ^o ). Since all topographic maps incorporate the geographic coordinate system, these coordinates are depicted at the four corners of a map sheet.

When reading the location of a position using the geographic coordinate system, latitude is expressed first then longitude.

Example:

33 ^o30' north latitude

117 ^o 15 ' west longitude

The most common type of USGS topographic map is at a scale of 1:24,000 which correlates to 7'30" of area coverage in latitude and longitude, hence the name "7.5 Minute Quadrangle." Minutes and seconds are noted along the border of the map at an interval of 2'30". By connecting the tic-marks along east and west side of the map and those along the north and south side of the map, a geographic coordinate system grid can be overlain upon your map that will allow you to determine the coordinates of a point on your map using the following method:

1. Determine which of the geographic coordinate system "grids" the position is in. Write down the degree and minute value in latitude and longitude for that grid (from the bottom right hand corner of that grid).

2. Determine the latitude to the nearest 10 seconds by laying a ruler over the point and the lines of latitude above and below the point, insuring that the straight edge is perpendicular to those lines of latitude.

Note: When measuring latitude and longitude you may notice that the grids of your geographic reference system do not have the same measurements, especially when comparing the measurements of longitude along the bottom of your map and the top of your map. This is due to the curvature of the earth, remember that all lines of longitude converge at the poles. Use care by measuring the sides of the geographic reference system grid in which your point lies and do not assume that all measurements are the same over the entire map.

3. Interpolate the latitude of the position by measuring the distance between those two lines of latitude on your ruler (the distance should be approximately 7.5 inches). Knowing the number of minutes and seconds of latitude the side of your geographic reference system grid is, (2'30" or 2.5') you now need to convert that to seconds to achieve an accuracy to the nearest 10 seconds. This is done by knowing there are 60 seconds in a minute, thus 2'30" is the same as 150 seconds, now divide this by 10 (precision to the nearest 10 seconds) resulting in 15. Divide 7.5 inches by 15, which equals 0.5. Therefore, you now know that every ½ inch on your ruler corresponds to 10 seconds of latitude for this particular geographic reference system grid on your map.

4. Measure the distance from the lower line of latitude to your point and determine its position of latitude ( in the northern hemisphere latitude is read from south to north). It is easy to interpolate your measurement further. If a ½ inch equals 10 seconds of latitude, then ¼ inch equals 5 seconds of latitude and so on. Write down the seconds value for the point's position of latitude.

5. Repeat the same procedure to determine the point's position of longitude to the nearest 10 seconds by now laying the ruler over the point and lines of longitude to the east and west of the point, insuring that the straight edge is perpendicular to those tow lines of longitude.

6. Interpolate the longitude of the position by measuring the distance between those two lines of longitude on your ruler ( the distance should be approximately 5.75 inches). Knowing the number of minutes and seconds of longitude the side of your geographic reference system grid is, (2' 30" or 2.5') you now need to convert that to seconds to achieve an accuracy to the nearest 10 seconds and divide that figure by 10. The answer is 15, now divide 5.75 by 15, which equals 0.383, (which is approximately the same as 3/8 inches). Therefore, you now know that every 3/8 inches on your ruler corresponds to 10 seconds of longitude for this particular geographic reference system grid on your map.

7. Measure the distance from the line of longitude to the east of your point (in the western hemisphere longitude is read from east to west). It is easy to interpolate your measurement further. If 3/8 inches ( which is the same as 6/16 inches) equals 10 seconds of longitude, then 3/16 inches equals 5 seconds of longitude.

8. Complete the geographic reference system coordinates for the point by recording the seconds measured in the point's position of longitude.

As you can see the geographic reference system is rather cumbersome for determining rather precise locations, thankfully there are other reference systems that have been developed for this task. Nevertheless, it is a reference system that is applicable the world over, the same can not be said for the next reference system we will discuss, the township and range survey system.

2. Township and Range Survey System: The federal government land office survey system was established in 1812 to facilitate the surveying and selling of land in the newly acquired lands west of Ohio. It is a system unique to the mid western and western portions of the U.S. As the area became consolidated into territories and eventually into states, the land there was divided into 6 mile square units of land. Each 6 square mile unit was numbered corresponding to its position relative to a parallel of latitude that served as the base line of the survey, as well as a selected meridian of longitude called a principal meridian (not to be confused with the Prime Meridian). Thus each 6 mile square piece of land was designated as either north or south and east or west. The north or south designation is referred to as township and the east or west designation is referred to as range. The entire 6 mile square piece of land, however, was referred to as a township. Each 6 mile square piece of land was further subdivided into 36 1-mile by 1-mile units called sections. Each of the 36 sections are designated numerically beginning in the northeast corner of the township. Each section can be subdivided still further into halves and quarters.

Determining Positions using the Township and Range Survey System: Most USGS topographic maps of the mid-western and western regions of the U.S. portray the township and range system. It is depicted in red and appears as a system of squares (approximately 3 inches on a side for a 1:24,000 scale map), each square having a number in the center.

1) Determine the township as well as the section of that township within which a particular point lies, and write them down on a piece of paper.

2) Next, using a non-permanent marker (alcohol markers are preferred) draw two lines that dissect that section into halves, both north to south and east to west. The section is now divided into a northwest, northeast, southeast, and southwest corners.

3) Further reduce each quarter of the section into quarters. Each section quarter is now divided into a northwest, northeast, southeast, and southwest corners.

Once this grid has been drawn over the section within which the point lies, you are ready to express the location of the point using the township and range system.

1) Placing the tip of your marker on the point, working from bigger to smaller, determine which corner of the section the point is in, and write that down next to the township and section determined earlier.

2) Keeping the tip of your marker on the point, and still working from bigger to smaller, determine which corner of the section corner the point is in and write that down next to the township, section, and section corner determined earlier.
Even though you will mainly be working with the above mentioned two reference systems, it is a good idea to have an understanding of other reference systems that are in use and are applicable over a wide area of the world's surface.

3. Universal Transverse Mercator Grid System (UTM): As the lines of latitude and longitude are curved (as is the earth), they are not depicted well on flat surfaces (such as a maps). The sections of the earth enclosed by intersecting latitude and longitude lines are not all of the same size and shape, this is particularly true in the extreme northern and southern areas of the earth. These problems complicate the location of points and measurements of directions. To overcome these problems a rectangular grid is made out of the earth's surface, between 84 degrees north latitude and 80 degrees south latitude. It divides the earth's surface into 60 UTM grid zones. Each zone is 6 degrees in longitude and numbered from 1 to 60, west to east, beginning at 180 degrees longitude (the international date line). This system then divides the earth's surface into 20 zones by latitude, each of which is 8 degrees in latitude and lettered from C to X (the letters I & O are omitted) beginning at 80 degrees south latitude. Note: Row X is 12 degrees in latitude. Thus, this portion of the earth's surface has been divided into 1,200 areas each of which can be identified an alpha-numeric label called a grid zone designation. An area's grid zone designation is determined by reading right and then up.

4. The Military Grid Reference System (MGRS): MGRS enables greater accuracy in expressing locations by taking the UTM system and breaking it down into smaller units of measure.

100,000 Meter Grid Squares

: Is transposed over the UTM grid zone and labeled with tow letters. The first letter identifies the column in which the square is in, the second letter identifies the row.

Grid Lines: Are then transposed over the 100,000 meter squares at an interval of 1,000 meters, and are labeled with two bold face numbers. The lines are numbered from 00 to 99, west to east, and south to north within each 100,000 meter square.

USGS topographic maps are not usually provided with a MGRS grid, but the northings and eastings values are provided along the borders of the maps at 1000 meter intervals. Example: ⁵57.

Do Exercise A

B. Determining Elevations: The main advantage of a topographic map is that it portrays the elevations and relief of the portion of the earth's surface it depicts.

Elevation: Is the vertical distance of a position above or below a datum plane. The datum plane for topographic maps is usually mean sea level. Elevation can be depicted in feet or meters, and is read from the value of the contour lines.

Relief: Is the representation of the shapes of natural terrain features (the shape of the ground).

1. Methods of Depicting Elevation and Relief

Layer Tinting: This is a method of showing relief by color where a different color is used to represent each band of elevation. This method does not allow for precise measurement of elevations at any given point.

Form Lines: These are dashed lines used to give a general idea of the relief only. They are not measured from any datum plane and are not labeled with elevation values.

Shading: Shading is a method of showing relief by using different tones of a color. The darker the shading the steeper the slope or the higher the elevation. Shading is often used in elevation guides found on NIMA maps.

Hachures: These are tic-marks used to depict rocky outcroppings, depressions, cuts, and fills.

Contour lines: Contour lines are the most common method used to depict relief and elevation. A contour line is an imaginary line on the ground above or below a datum plane, which most commonly is sea level. The three types of contour lines are:

Index: Starting at mean sea level (zero), every fifth contour line is a heavier line with elevation for that line printed on it. For most 1: 24,000 maps the contour interval is 10 feet, thus the index contour lines are every 50 feet.

Intermediate: These are lighter contour lines that fall in between the index contour lines and do not have the elevation printed on them.

Supplementary: These are dashed lines used to show sudden changes in elevation of at least on half the value of the contour interval.

2. Using Contour Lines to Determine Elevation:

1) Determine the contour interval of the map.

2) Select a point on your map.

3) Find the two index contour lines the point lies between. The index contour line with the higher value can be said to lay above the point, and the lower value index contour line lies below the point.

4) Determine the elevation of the point by choosing either the index contour line that lies above your point or the one that lies below, and count the number of intermediate contour lines from the index contour line to the point. Remember, if you are starting from the index contour line that lies above your point, you will be moving down-slope towards your point as you count the intermediate contour lines, and you will have to subtract the contour interval from the index contour line value for every intermediate contour line crossed.

5) If the point is exactly on a contour line then the elevation of the point is expressed as the value for that contour line. More than likely it does not lay on a contour line but in between two contour lines. There are differing schools of thought on how to handle these situations, suffice it to say that you can either apply the value of the contour line to which the point is closer as the points elevation, or you can add or subtract (depending if you were tracing up-slope or down-slope) one-half the contour interval from the adjacent contour line's value and assign that as the point's elevation.

3. Other Methods of Depicting Elevation and Relief:

Bench Marks: Bench marks (BMs) are surveyed elevations at specific points. They can be monumented or not. Refer to the map legend for the symbol for a bench mark.

Spot Elevations: These are points that may be surveyed and are used to depict elevations at prominent terrain features, such as hill tops and road intersections. Refer to the map legend for the symbol for spot elevations.

C. Determining Terrain Features

Although the use of contour lines provides a more scientific and accurate portrayal of elevations, the relief that is depicted by contour lines can be difficult to visualize in 3-D. In order to assist the map reader in visualizing the terrain the following examples are provided.

1. Examples of Terrain Features

Hills: Hills are depicted by closed rings of contour lines that get successively smaller towards the top of the hill.

Valley: A valley is a stretched out groove in the land usually formed by streams or rivers. A valley begins with high ground on three sides and usually has level ground of a lower elevation at its bottom where the water course is found. Contour lines forming a valley are either 'U' or 'V' shaped with the closed end of the V points upstream towards higher ground.

Ridge: A ridge is a sloping line of high ground. The contour lines forming a ridge tend to have a 'U' or 'V' shape with the closed end point away from the high ground.

Depression: This a low point in the ground or a sinkhole surrounded by higher ground all sides. It is depicted by closed contour lines with hachures pointing inward toward the lower ground.

Draw: A draw is a less developed stream course than a valley. It has high ground on three sides with no level ground in the draw. It is depicted by 'U' or 'V' shaped contour lines, with the closed end of those lines pointing towards the top of the draw (higher ground).

Spur/Finger: This is a sloping line of higher ground with lower ground on three sides. It is depicted by 'U' or 'V' shaped contour lines with the closed end of those lines point towards the bottom of the finger (lower ground).

Cliff: This is a vertical or near vertical abrupt change in the land. It is depicted by very closely spaced contour lines, or by converging contour lines into one contour line that is some times marked with hachures that point toward the lower ground.

Cut: This is a man-made terrain feature created by digging through high ground, usually for transportation routes. It is depicted by a contour line drawn along the cut line with hachures pointing toward the lower ground.

Fill: Fill is also a man-made terrain feature resulting from the filling of a low area, usually to accommodate transportation routes. It is depicted by a contour line drawn along the fill line with hachures on the contour line pointing toward lower ground.

As we have discussed earlier, relief is basically the shape of the land. As such, the spacing of the contour lines also tells much about the relief. For example, you already understand how contour lines can represent a hill, but how steep is the hill and what type of slopes can be found on the sides of the hill? The following are provided to assist you in answering such questions.

2. Types of Slopes:

Uniform Gentle: This type of slope is depicted by contour lines that are evenly spaced and wide apart.

Uniform Steep: This type of slope is depicted by contour lines that are evenly spaced and close together.

Concave: This type of slope is depicted by contour lines that are close together towards the top of the terrain feature and are widely spaced towards the bottom of the slope.

Convex: This type of slope is depicted by contour lines that are widely spaced towards the top of the terrain feature and are close together towards the bottom of the slope.

Do Exercise B

D. Scale and Distance

A topographic map is a reduced 'picture' of the ground it represents. In order to show the ground exactly as it appears, your map would have to be life size. This is unreasonable, so map makers use "scale" (usually expressed as a representative fraction or as a graphic bar scale) when making a map.

Representative Fraction: This gives the numerical value of the scale for a map. The most common USGS topographic maps have an RF scale of 1: 24,000. The RF is always written with the map distance as 1. It is independent of any unit of measure (it can be used for yards, meters, inches, and the like). An RF of 1:24,000 means that one unit of measure on the map is equal to 24,000 of that same unit of measure on the ground. For example, 1 inch on your map is equal to 24,000 inches (or 2,000 feet) on the ground.

Graphic Bar Scale: A graphic bar scale is a sort of ruler that depicts both metric and English units for measuring distance on a map. One must become proficient at expressing distances in both units of measure. Each bar scale is divided into two parts:

The Primary Scale, which is to the right of zero and is marked in full units of measure. Example: 1 mile, 2 miles, 3 miles, etc.

The Extension Scale, which is to the left of zero and is marked in tenths of units of measure. Example: 1/10th mile, 2/10th mile, etc.

Note: 10 tenths of a mile equal 1 mile, and there are 1000 meters in a kilometer.

E. Measuring Distances

Measuring Straight Line Distances: Mark the position of two points on your map with a marker. Lay a piece of paper along the two points and mark the paper where each point touches it. Transfer the paper to the graphic bar scale and measure the distance in the appropriate unit of measure.

1) First place the left most tick mark on the zero of the graphic bar scale and count the number of full units of measure towards the right hand tick mark.

2) More than likely, the distance will not correspond exactly to a full unit of measure. In that case, indicate on your paper edge the location and the number of the last full unit of measure attained.

3) Now, slide your piece of paper so that the right most tick mark (representing the second point from your map) is aligned with the zero on the same unit of measure, and count the number of tenths until you reach the mark you made in step 2. If this distance is not expressible in full tenths, then you will have to interpolate the value of the remainder between the tenths markers.

Measuring Irregular Distances: For measuring distances along curved features such as roads or streams, you can either use the edge of a piece of paper or a piece of string.

Using a piece of paper:

1) Make a tick mark at the starting point, of the distance you wish to measure, on the map and the paper.

2) Keeping those two tick marks aligned, rotate the piece of paper until it bisects the feature being measured and make another tick mark on the map and the paper. This will enable you to measure around the curves in a road or bends in a stream.

3) Continue doing this until the entire distance has been covered. Ensure that you keep the appropriate tick marks on the map and paper lined up.

4) Transfer the paper to the appropriate bar scale and measure the distance.

Do Exercise C

F. Determining Directions

1. North

As seen above in the discussion of the declination diagram, there are three different norths that can be used as the base direction for angular measurements; grid north, magnetic north, and true north.

Grid North: Is established by the UTM and MGRS systems. Grid north is depicted in the declination diagram by a line with the letters GN (grid north) above it. Military maps produced by DIMA (Defense Imaging and Mapping Agency) are oriented to grid north.

Magnetic North: Is the direction to the north magnetic pole which is located in the vicinity of the Hudson Bay, Canada. This is the direction that compass needles point. Magnetic north is depicted in the declination diagram by a line with a half arrow with the letters MN (magnetic north) above it.

True North: Is a line from any point of the earth's surface to the north pole. All lines of longitude are true north. True north is depicted in the declination diagram by a line with a star. The top of USGS topographic map sheets are oriented to true north.

Why do I need to know the difference between the 3 norths? The difference between the 3 norths becomes critical when one is using a map in conjunction with a compass to navigate from one place to another. For example; airline pilots naturally use maps to determine the route by which they will fly to get from San Diego to Kansas City. They will plot this route as directions upon a map, as angular deviations from true north. However, they will be using a compass in their airplane to guide them along their course, and the compass expresses angular deviations from magnetic north. Look at the declination diagram on the Lenexa Quadrangle, USGS topographic map sheet. Note the numbers that are written to the left and to the right of the declination diagram. These represent the difference, on this map sheet, between true north and grid north and also between true north and magnetic north. As you can see, just on the Lenexa Quadrangle there is a difference of 4 degrees between true north and grid north. In many areas of the world this difference is significantly greater. Now, let's go back to our airline pilots. If they did not compensate for this difference between the direction they plotted on their map (a true north direction) and the direction that will be indicated by their compass (magnetic north direction), the route of their flight would miss Kansas City by a substantial margin.

3. Methods of Expressing Directions: Map users need a way of expressing directions that is accurate, adaptable to any part of the world, and has a common unit of measure. Directions are expressed as the units of angular measure from a base direction of north or zero.

Degrees: The most common unit of measure is the degree, with its subdivisions of minutes and seconds. There are 360 degrees in a circle, 60 minutes in a degree, and 60 seconds in a minute.

Note: Most compasses and protractors are delineated in degrees only and not minutes and seconds.

Mil: Another unit of measuring angular deviations is the mil. It is a more accurate unit of measure as there only 360 degrees in a circle, but there are 6400 mils in that same circle. Thus, there are 17.78 mils in a degree.

Cardinal and Inter-cardinal directions: There are four cardinal and four inter-cardinal directions.

Cardinal: North, South, East, and West

Intercardinal: Northeast, Southeast, Southwest, and Northwest

When expressing directions with maps, it is common to refer to those directions as azimuths, of which there are three types;

Grid Azimuths: When an azimuth is measured on a map using the UTM and MGRS systems, between two points, it is referred to as a grid azimuth.

Magnetic Azimuths: This refers to directions as indicated by a compass.

True Azimuths: When an azimuth is measured on a map using the lines of longitude, it is referred to as a true azimuth.

2. Determining Azimuths: The two tools used to determine azimuths are the protractor and the compass. A protractor is used to determine grid and true azimuths and a compass is used to determine magnetic azimuths.

Using a semi-cirular protractor:

1) Draw a line on your map connecting the two points that you wish to measure the direction from and to.

2) Place the protractor on the map so that the tick marks indicating 180 degrees on the protractor are parallel to one of the lines of longitude you drew on your map earlier.

Note: Being a semi-circle, the protractor can only measure values between 0 degrees and 180 degrees. Thus, it will be necessary for you to determine which way to lay the protractor (with the measurements to the left or to the right) based upon the general cardinal or inter-cardinal direction the line between the two points follows. Care must be taken when measuring the angular deviation when the protractor is used with the scale facing to the left as the user will have to be aware that only the numbers between 0 degrees and 180 degrees are portrayed. (Add 180 degrees to all measurements taken with the protractor scale facing to the left)

3) Keeping the 180 degree tick marks of your protractor parallel to the lines of longitude, slide the protractor until the point from which you wish to measure the azimuth is exactly under the tick mark located in the base of the protractor.

4) Determine the true azimuth by observing where your line between the two points intersects the protractor's scale and recording that value.

Using a square protractor:

1) Carefully poke a hole into the protractor at the intersection of index lines (at the center of the protrator) and insert a piece of string and tie it off.

2) Next, place the protractor on the map so that the verticle index line is parallel to the lines of longitude you drew on your map earlier in the module.

3) Keeping the verticle index line of the protractor parallel to the lines of longitude, slide your protractor so that the point from which you wish to determine the true azimuth from is directly underneath the intersection of the horizontal and verticle index lines (the center of the protractor).

4) Holding the protractor in place, draw the string out to the point you wish to determine the true azimuth to.

5) Read the true azimuth to that point from the appropriate outer scale of the protractor. The outer scale is in mils and the inner scale is in degrees.

Note: Make sure that you are placing the protractor on the map so that the outer scales can be read in a clockwise manner.

Using a compass: In order to follow a true azimuth by using a compass, you will first need to convert the true azimuth to a magnetic one.

1) Convert the azimuth you attained using the protractor and string by applying the magnetic declination from the declination diagram to the true azimuth using the LARS (Left Add Right Subtract) method.

For example, let's say that you determined the true azimuth to be 90 degrees (or 1600 mils).

2) Note the magnetic declination from the declination diagram. For all of the four quadrangles of the Kansas City area, the magnetic declination is 4 degrees or 71 mils.

3) The acronym LARS stands for Left Add, Right Subtract, and refers to which side of true north magnetic north lays in the declination diagram. In this example you are converting a true azimuth to a magnetic azimuth. So, place your finger on the true north line of the declination diagram and then move your finger to the magnetic north line. Which way did you move your finger, left or right? You moved your finger to the right.

Now apply the LARS method, you moved your finger to the right and LARS states, right subtract. Therefore, you will need to subtract the magnetic declination from the true azimuth determined in step 1.

Degrees 90 - 4 = 86

Mils 1600 - 71 = 1529

4) This results in magnetic azimuths that you would then follow on your compass to navigate from point A to point B.

Do Exercise D (optional)

IV. Advanced Topographic Map Interpretation

A. Terrain Profiles

Terrain profiles enable users to more readily discern the relief of an area by constructing a cross-section along a predetermined line.

1) Select a portion of your map that where a stream is flowing. Place the edge of a piece of paper onto a topographic map perpendicular to the stream's course and note how the contour lines intersect the edge of paper.

2) Carefully mark the edge of the paper at every place a contour line crosses the edge of the paper. Do this along a line approximately 4 to 6 inches in length.

3) Carefully mark each of the tick marks on your paper with the value of that contour line. Also, it may be helpful to record the location where major highways and streams intersect the paper.

4) Transfer your piece of paper with the tick marks to the graph paper. On the graph paper you will need to construct a vertical scale by noting the lowest and highest elevations recorded on your tick marks. You will also need to note the contour interval from the map, and be sure to allow for a full contour interval below the lowest recorded elevation and also above the highest elevation.

5) Place your piece of paper below your vertical scale and align it with a horizontal line on the graph paper.

6) Now you will need to transfer the tick marks and their corresponding elevations to the graph paper. This is done by placing the tip of your pencil onto the first tick mark and reading the elevation value. Then trace up the graph paper and place a dot directly over your tick mark at the appropriate place on the vertical scale.

7) Once this is completed for all of the tick marks, you will need to connect the points on the graph paper, which results in a terrain profile along that segment of the map.

Look at your profile and try to identify the following; areas of high ground, areas of low ground, the type of slope leading from the high ground to the low ground. Using arrows, show in which direction run-off would occur if it were to rain over the section of the map depicted by your terrain profile.

Note: Profiles done in this manner result in profiles that are called 'vertically exaggerated', in other words the high points and low points are not to scale. However, this technique does enable a better vision of the relief of the land.

Do Exercise E

B. Delineating a Watershed

What is a watershed? A watershed is that area of land, if rained upon, that would result in run-off entering a particular stream. The extent of the watershed is dependent upon the scale observed. The watershed of the Mississippi River is larger than that of the Missouri River. This is because the Missouri River's watershed is part of the Mississippi River's watershed, which is due to the fact that the Missouri River flows into the Mississippi River.

Let's look at the four topographic quadrangles of Kansas City. Find the Missouri River and the Kansas River. Observe how the Kansas River flows into the Missouri River. Each river has its own watershed upon which if rain should fall, the resulting run-off would enter either the Missouri or Kansas Rivers. The Kansas River, however, is a tributary to the Missouri River and as such, is part of the Missouri River's watershed.

Now let's look at Brush Creek. Beginning with the head waters (the upstream end) of Brush Creek on the Lenexa Quadrangle, trace its course until it enters the Blue River. Note the other streams that flow into Brush Creek along its course. Each one of these streams has its own watershed, which is part of the Brush Creek watershed. We have already noted that Brush Creek flows into the Blue River (on the Kansas City Quadrangle), so Brush Creek is part of the Blue River's watershed. Further, although it is not depicted on the topographic maps that you are using, the Blue River flows into the Missouri, so the Blue River is part of the Missouri River's watershed. Eventually, the rain that fell on the Brush Creek watershed and resulted in run-off entering Brush Creek would enter the Mississippi River (since the Missouri flows into that river) and make its way to the Gulf of Mexico.

This is an overly simplified description, but it should give you the fundamentals you will need to delineate the spatial extent of a watershed on a topographic map.

Watersheds are very important geographic features as well as ecological units. Earlier, you used a terrain profile to show how run-off would flow down the slopes of higher ground to a stream, now you will map the spatial extent of a watershed. Understand, that streams flow from areas of higher elevation to areas of lower elevation, and that streams are normally found in valleys. Valleys are terrain features where lower ground is surrounded on two to three sides by higher ground. The local extent for a stream's watershed can be found by looking at the higher ground surrounding a stream and determining whether run-off would flow into the stream or not. If the answer is yes, then that area is part of a stream's watershed. You will need to study the map carefully, using all of the knowledge you have gained about terrain features, contour lines, and slopes to plot the extent of a watershed.

Note: There is no contour line at the top of terrain features such as hills and ridges, so you will need to try and visualize the crest of the hill and place your line marking the extent of the watershed accordingly.

Do Exercise F

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