Scale (Relational Fraction; Graphical)Elevation contours (Relative to M.S.L)Boundary (Latitude & Longitude)Color (Water bodies, Woodlands, etc.)Cultural Features (man-made features)
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Features of Topographic Maps Scale (relational fraction RF; Graphical scale in metric and imperial units). Elevation contours (relative to mean sea level), spot elevations, benchmarks. Latitude and Longitude boundary (example: 7.5 x 7.5 minute maps at 1:24,000 scale). Color (Blue=water; green = vegatation; etc.) Cultural features (buildings, roads, etc.).
Scale
Relational fraction 1:24,000 1 inch on the map = 24,000 inches in reality 1 inch on the map = 24,000 inches x 1 foot/12
inches 1 inch on the map = 2000 feet 1 inch on the map = 2000 feet x 1 mile/5280 ft 1 inch = 0.378 miles
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Relational Fraction (RF) Should be conceptualized as a ratio of the paper map to reality. For example on a 1:24,000 scale map 1 inch on the paper map = 24,000 inches in reality. From the above starting statement any useful scale may be derrived: 1 inch on the map = 24,000 inches in reality 1 inch on the map = 24,000 inches x 1 foot/12 inches 1 inch on the map = 2000 feet 1 inch on the map = 2000 feet x 1 mile/5280 ft 1 inch = 0.378 miles
Graphical Scale
Uses a graphical scale to indicate distances
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Graphical Scale All topographic maps should have a graphical bar scale that documents the scale of the map. This is especially important when the map is reproduced or projected at a scale different than the original paper map – in whch case the RF will not be correct. U.S. government maps normally have graphical scales in imperial and metric units.
Elevation ContoursContour lines (brown) = points of equal elevation. Based on aerial photographs analyzed
stereographically Must agree with benchmarks and spot elevations Contour interval (C.I.): elevation change between
adjacent contours Hachured contours indicate closed depressions Zero contour is always mean sea level Index contours = 5 x C.I.
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Elevation Contours Contour lines (brown) = points of equal elevation. 1. Based on aerial photographs analyzed stereographically 2. Must agree with benchmarks and spot elevations 3. Contour interval: elevation change between adjacent contours 4. Hachured contours indicate closed depressions 5. Zero contour is always mean sea level. 6. Index contours = 5 x C.I.
Construction of Topographic Contours
Contours of any parameter use a simple proportionality rule.Contours should “V” in the upstream direction across valleys.
x
xx
x80
80
87
77
flow
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Construction of Topographic Contours: 1. Contours of any parameter (including elevations) use a simple proportionality rule (see above). 2. Contours should “V” in the upstream direction across valleys. 3. Note that streams flow opposite the direction “pointed” by the “V” in topographic contours.
Topographic contours in 3D
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Topographic Contour Rules: 1. When contours lines cross streams, they will always form a V-shape that points toward the upstream (higher elevation) portion of the stream valley. 2. Contours do not intersect or merge unless the ground surface is vertical or has a negative slope. Because this is rare in nature, you will not usually encounter this situation in the lab unless you are investigating man-made topographic structures. 3. Closed contours that form circular or elliptical patterns represent locally high areas that are termed hills or hogbacks. 4. Closed contours that are marked by short tic marks- termed hachures -indicate a bowl-shaped depression. The hachures are always on the lower elevation side of the contour and point toward the bottom of the depression. 5. Steep slopes are indicated by closely spaced contour lines, while low slopes are indicated by widely spaced contours. Furthermore, if contour lines are straight and maintain a constant spacing, a planar inclined surface is indicated. 6. The difference between the lowest and highest points on the map is termed the topographic relief of that area. 7. A change of slope direction will cause a repeat of at least one contour line in the direction of travel. Imagine that you were traversing a hill with an elevation of 105 feet. On a topographic map you would have to cross the 100 foot contour line twice- once going uphill, the second time while traveling downhill.
Topographiccontours in 3D cont.
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Note that the flood plain adjacent to the stream is defined by the widely spaced contours. The flooding extents of a specific rise of a river in flood stage can be easily predicted with a topographic map.
Contours: can delineate geological contacts
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The “hogback” in the above photo would form a discontinuous ridge line on a topographic map. The “strike” of the planar unit would be parallel to the trend of the ridge line. The “dip-slope” defined by contour lines would quantify the true dip angle.
Topographic Map Boundary
Always consist of lines of latitude and longitudeContain tick marks of UTM and SPCS on the border 32 7’ 30’’
32 15’
103 22’ 30’’103 30’32 7’ 30’’
32 15’103 30’ 103 22’ 30’’
7.5’ TopographicQuadrangle border (1:24,000)
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Topographic Map Boundary 1. Always consist of lines of latitude and longitude. 2. Contain tick marks of UTM and SPCS on the border. 3. Note that the map border is longer in N-S extent than E-W extent. This is an effect of the map projection and becomes more pronounced with increasing distance from the equator.
Topographic Map ColorsBrown: topographic contoursGreen: Forest and/or wetlandsWhite: cleared areas (i.e. pastures, etc.)Black: Cultural features (buildings, roads)Red: Land office grid system (Township & Range system); Major road systemsMagenta: Photo-revised areasBlue: water bodies
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Topographic Map Colors: 1. Brown: topographic contours 2. Green: Forest and/or wetlands 3. White: cleared areas (i.e. pastures, etc.) 4. Black: Cultural features (buildings, roads) 5. Red: Land office grid system (Township & Range system); Major road systems 6. Magenta: Photo-revised areas 7. Blue: water bodies
Topographic Map Examples
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Topographic Map Examples: Springhill Quadrangle. Note the coordinate systems documented along the margin of the map: UTM coordinates. SPCS coordinates. Latitude-Longitude coordinates. Land Office Grid (LOGS) System (Township-Range). Note specific symbols on the map denoting coordinate system reference points.
Map Coordinate Systems
Land Office Grid System (LOGS) (Township & Range)Universal Transverse Mercator (UTM)State Plane Coordinate System (SPCS)
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Map Coordinate Systems: 1. Land Office Grid system (Township & Range). 2. Universal Transverse Mercator (UTM). 3. State Plane Coordinate System (SPCS). 4. Geographic (Latitude and Longitude).
• Note that because of projection geometry UTM zones can extend to 84N and 80S.
• Each 8 degrees of latitude is divided into alphabetical zones for quick identification – zone 18T includes New York city in the above example.
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UTM Zones: Note that because of projection geometry UTM zones can extend to 84N and 80S. Each 8 degrees of latitude is divided into alphabetical zones for quick identification – zone 18T includes New York city in the above example.
UTM CoordinatesThe origin point of each UTM zone is where the central meridian of the zone crosses the equator. Each UTM zone spans 6 degrees of latitude with the central meridian 3 degrees from both the east and west bounding meridian of the zone. For example, UTM grid zone 16 spans the 90W to 84W longitude. The x origin is therefore 87W.X coordinates (easting) are in meters offset from the central meridian plus 500,000 of false easting to ensure values are positive.Y coordinates (northing) are meters offset from the equator in the northern hemisphere; in the southern hemisphere 10,000,000 meters minus the offset from the equator so that values are positive and increase to the north.All offsets are calculated with the transverse Mercator projection (Equal Area).
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UTM Coordinates: 1. The origin point of each UTM zone is where the central meridian of the zone crosses the equator. Each UTM zone spans 6 degrees of latitude with the central meridian 3 degrees from both the east and west bounding meridian of the zone. For example, UTM grid zone 16 spans the 90W to 84W longitude. The x origin is therefore 87W. 2. X coordinates (easting) are in meters offset from the central meridian plus 500,000 of false easting to ensure values are positive. 3. Y coordinates (northing) are meters offset from the equator in the northing hemisphere, 10,000,000 meters minus the offset from the equator so that values are positive and increase to the north. 4. All offsets are calculated with the transverse Mercator projection (Equal Area).
UTM Coordinate Calculation
Calculation of UTM coordinates is not trivial! Rarely would they be calculated by hand.The exact calculation also depends on the map datum projection – therefore UTM coordinates based on NAD27 datum are different that NAD83 for the same position on the Earth.
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UTM Coordinate Calculation: 1. Calculation of UTM coordinates is not trivial! Rarely would they be calculated by hand. 2. The exact calculation also depends on the map datum projection – therefore UTM coordinates based on NAD27 datum are different that NAD83 for the same position on the Earth.
UTM Coordinate Calculation: Object Pascal See above procedure. Note that no false easting or northing is added by the procedure. In the procedure easting is calculated in the “x” variable, northing in the “y” variable.
State Plane Coordinate System (SPCS)
Each state in the U.S. defines its own projection system (feet units).The origin is chosen to always produce positive eastings and northings (x and y).The projection varies depending on the state- whatever tends to minimize distortion is chosen.False easting or northing may be added.Large states may have several different “zones” each with their own origin point. For example, FL has east, north and south zones.Because each SPCS is unique a topographic map that is near a transition may have more than one SPCS documented along the map margin.
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SPCS: 1. Each state in the U.S. defines its own projection system (feet units). 2. The origin is chosen to always produce positive eastings and northings (x and y). 3. The projection varies depending on the state- whatever tends to minimize distortion is chosen. 4. False easting or northing may be added. 5. Large states may have several different “zones” each with their own origin point. For example, FL has east, north and south zones. 6. Because each SPCS is unique a topographic map that is near a transition may have more than one SPCS documented along the map margin.
GPS and Coordinate SystemsMost GPS receivers will have geographic and UTM coordinate systems defined, along with variations in map datum that are selectable.SPCS may or may not be included.UTM coordinates are preferred for navigation in the field if positions are plotted on a map because the density of the UTM grid marks make plotting very accurate.Plotting of geographic coordinates on a physical map requires a specialized grid not generally plotted on paper or digital maps. Waypoints should be stored as geographic coordinates with at least 8 decimals of precession because they can be projected into any other type of coordinate systems.
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GPS and Coordinate Systems: 1. Most GPS receivers will have geographic and UTM coordinate systems defined, along with variations in map datum that are selectable. 2. SPCS may or may not be included. 3. UTM coordinates are preferred for navigation in the field if positions are plotted on a map because the density of the UTM grid marks make plotting very accurate. 4. Plotting of geographic coordinates on a physical map requires a specialized grid not generally plotted on paper or digital maps. 5. Waypoints should be stored as geographic coordinates with at least 8 decimals of precession because they can be projected into any other type of coordinate systems.
Land Office Grid Example:Benchmark 212: NW ¼, NE ¼, sec.
36, T3S, R3W
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Actual LOGS location example: Springhill Quadrangle 1. Benchmark 212: NW ¼, NE ¼, sec. 36, T3S, R3W.
Exam SummaryFor upcoming exams be sure to review the below items from this lecture: LOGS coordinate system. UTM coordinate system. Geographic (Lat-Long) system. SPCS coordinate system. Be able to convert to-and-from RF values of scale. Be able to discuss index contours, contour intervals, topographic
contour lines. Graphical versus mathematical statements of scale. Know definitions of benchmarks, spot elevations, how to
construct topographic contours from benchmarks and spot elevations.
Know the meaning of different colors on topographic maps.
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Exam Summary: LOGS coordinate system. UTM coordinate system. Geographic (Lat-Long) system. SPCS coordinate system. Be able to convert to-and-from RF values of scale. Be able to discuss index contours, contour intervals, topographic contour lines. Graphical versus mathematical statements of scale. Know definitions of benchmarks, spot elevations, how to construct topographic contours from benchmarks and spot elevations. Know the meaning of different colors on topographic maps.
