Topographic Maps Contouring Topographic contours indicating surface relief Image taken from US Army training manual Solid yellow lines represent surface isobars line of equal air pressure Green dashed lines are geopotential heights the altitude at which 500 millibars of air pressure are at ID: 511297
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Slide1
Standard 1.h: Read and interpret topographic and geologic maps.
Topographic MapsSlide2
Contouring
Topographic contours indicating surface relief. Image taken from US Army training manual.
Solid yellow lines represent surface isobars, line of equal air pressure. Green dashed lines are geopotential heights, the altitude at which 500 millibars of air pressure are attained. These types of contour maps are used by meteorologists. The weather system shown is the Storm of the Century, a powerful winter storm called a nor’easter.
In this lesson, you will learn about the ways to show three dimensions on a flat map, how to read topographic maps and other contour map types, and how to draw contours.Slide3
Topographic Maps
Detailed maps showing the elevations of hills and valleys of an area.Use lines, symbols, and
colors to represent changes in elevation
and
features on
Earth’s surface.
Topo
graphy = shape of the landSlide4Slide5
These
topographic maps
combine shading
,
color, and contour lines. Slide6
Contour Lines
Contour lines are used to
represent
the three dimensional surface of the world on a flat
map.
Can also be called isolines
or isopleths.
What do you notice about the map on the right?Slide7
A
contour line connects points of equal elevation.Elevation refers to the distance of a location above or below sea level.Contour lines never cross.Slide8
contour lines marked with elevation
Index ContoursSlide9
Contour Intervals
distance in elevation change between each contour lineSlide10
The contour interval is 20 ft. Point elevations are
:A = 700 ftB = 740 ftC = 770 ftD = 820 ft
Uphill
direction
Slow change in elevation. Contour lines
far apart.
Rapid change in elevation. Contour lines
Close together.Slide11Slide12
Widely spaced contour lines show a gentle slope. When they are close together, the slope is steep.
Spacing between Contour LinesSlide13
When the contour lines are close together at the top of a hill, the hilltop is pointed.
When the contour lines are widely spaced, the hilltop is flat.Slide14
Contour line rules
Contours are imaginary lines that join equal values of whatever is being mapped. For example, the 100 ft contour marks all areas on a map that are 100 ft in elevationContour lines are defined by a contour interval. The contour interval tells you the amount of elevation change between contour lines.
The contour interval for a map is constant unless otherwise noted.Slide15
When contour lines are close together, the change in elevation increases very quickly (steep).
When the contour lines are spread apart, the amount of elevation change is small (flat).Contour line rulesSlide16
You are to hike to the top of Blake Island.
Which side of Blake Island would be the steepest climb, the west coast or the north coast?
W
N
(The west coast because the contour lines are closely spaced. You have a very large amount of change in elevation over a short distance. Go to the north for a more gentle climb)Slide17
Contour maps allow you to interpret the “lay of the land”. From surveyors to soldiers, the ability to read the topography in a topographic map is essential. Review the following topographic maps and learn to identify the features shown.Slide18
The V’s point upstream in a draw. Where you see a draw in a topographic map you can reasonably assume there is or has been water flowing that
led to the erosion and migration of the contour lines.Slide19Slide20Slide21Slide22Slide23Slide24Slide25
Match the letter and numberSlide26
There are many types of contour maps
Topographic (relief) mapsBathymetric (sea floor elevation) mapsIsohyet (rainfall) mapsIsopach (rock or sediment thickness) mapsIsotach (wind speed) mapsIsobaric (air pressure) maps
Geopotential
height (elevation of a given air pressure) mapsSlide27
U.S. Geological Survey topographic map
Very common topographic mapEntire US covered by these mapsSize of each maps is 7.5 minutes by 7.5 minutes (30 minutes make 1 degree of longitude or latitude)
Scale of these maps is 1:24,000 (1 inch = 2000 ft/24,000 in)
Also known as a topographic quadrangleSlide28
Bathymetry map. Shows depth of seafloor. Slide29
Isobars (solid yellow lines) on an isobaric
map.This is a strong low pressure system, which produced large amounts of snow and wind across the eastern US.In an isobaric map, where isolines are close together, winds are the strongest. Winds are strongest in Virginia, North Carolina,and West Virginia.Green dashed lines are geopotential
heights, the altitude at which 500
millibars
of air pressure are attained.Slide30
Isohyet
map. Rainfall distribution on August 17th – 20th, 2002 (isohyets are in millimeters) Slide31
Isohyet map showing predicted rainfall in inchesSlide32
Isopach lines (contour interval = 5 ft) show the thickness of a rock layer known to produce oil. The round symbols are oil well locations and the depths (6000 – 7000 ft) drilled to reach oil. Slide33
Isopach map showing
thickness of the limestonecomprising the Florida AquiferSlide34
Colored areas represent
isotachs, lines encompassing areas of equal windspeed. Contour interval = 10 knots. The red area is a fast region of wind comprising of the polar jet stream. It flows from west to east, something that you cannot infer from this map unless the mapmakers were to plot wind barbs, arrows to indicate the direction of wind flow.Green lines are geopotential heights (air pressure).Slide35
These features are represented by different symbols.
A map legend explains what the symbols on a map represent.Topographic maps and most other maps include both human-made and natural features that are located on Earth’s surface.
Map LegendSlide36
A
map scale is the ratio between distances on a map and actual distances on the surface of Earth.Map Scales
When using a map, you need to know how to measure distances.Slide37
There are three types of map scales: verbal scales, graphic scales, and fractional scales.
A verbal scale expresses distance as a statement, such as “One centimeter is equal to one kilometer.” A graphic scale consists of a line that represents a certain distance, such as 5 km or 5 miles.
A
fractional scale
expresses distance as a ratio,
such as 1:63 500.
Map ScalesSlide38
What does it mean if a map says
“Scale 1:100 000”?This fractional scale means that one unit on the map represents 100 000 units on Earth’s surface. For example, one inch on the map would equal 100 000 inches on Earth’s surface.Slide39
This is a map of
geopotential heights. Contour interval is 60 meters.Note that the wind barbs in this map convey the direction of wind flow, which is predominantly west to east at this altitude.