Topographic Maps specialized maps which show the highs and lows (relief) of the Earth’s surface
topo map parts… • Field : A region in which similar quantities can be measured at every point or location (ex. temperature in a room or depth of snow) • Isolines: Connect points of equal values on a map • Contour line: Connect points of equal elevation
Index contour: A contour line that has elevation noted on it. Typically a multiple of five or ten (example: 300, 320, etc) • Contour interval: The difference in the height between two contour lines that are next to each other. NOTE: A contour interval shows a difference in vertical height and a map scale shows horizontal distance : Contour Interval = 5 feet
Contour interval = (Index Contour 2-Index Contour 1)/ Number of Lines between Ex.: (320-300)/4= 20/4= 5 ft contour interval
…topo map parts • A benchmark is a point where the actual elevation is known • elevation is shown on the map by the letters BM and the elevation next to it (ex. BM1078) • .
Depression contours show where the elevation decreases (a hole, volcano crater, etc.) • When reading the depression contour, the elevation of the first one is the same elevation of the regular contour before it. The next one decreases the same amount as the contour interval
Depression contours are shown with dashed lines inside of the contour line circles
Contour lines Index contour benchmark
Landforms on Contour Maps • The steepness of an area is shown by the closeness of the contour lines • The closer the contour lines are together, the steeper the area (cliff, etc.) • When the contour lines are spread out, the land is relatively flat. • A closed circle after a series of increasing contour lines shows the top of a hill or mountain
Steep slope (close lines) Hill top (circles) Gentle slope (spread out lines)
Landforms on Contour Maps • contour line crosses a stream or river, the contour line bends and forms a “V” shape SUPER IMPORANT!!!!!!!!!!!: • The point of the “V” shows the direction that the water is coming from • The “v” points to the SOURCE of the river or upstream
The “V” points to the source, so the river is flowing in what direction??? Note the “V” shape of the contour lines as they cross the river!
Escarpments and Slope • Escarpments: Another word for cliff
The slope or gradient of the hill can be determined by using your ESRT Gradient = difference in elevation ------------------------------------------------------------------------------- distance
Some important points • Contour lines are circles within circles • Contour lines never cross each other, but they may touch • Contour lines are darker every 5th line and has elevation printed
Contour lines are not spaced evenly. • The closer the lines, the steeper the slope • The smaller the circle towards the middle, the closer you are to the top of a hill
Some important points • Hachured/dashed lines show a depression or a hole (decrease in elevation) • The first contour line of a depression is the same elevation as the contour line which surrounds it • When lines cross a stream, they bend making a “V” • The “V” points upstream, opposite the direction of flow.
Profile:side view of the hill/mountain; drawn by using a contour map and by plotting the elevations of certain points on a vertical axis
Making a Profile from a Topographic Map • Lay a piece of scrap paper along the line where the profile is to be constructed. • Make a mark on the scrap paper at the exact place where each contour line, stream and hill top crosses the profile line. • Label each mark with the elevation of the contour it represents.
d. On the graph provided, label the horizontal lines with matching elevations, if not already completed for you e. Place the scrap paper with the labeled contour lines at the bottom of the graph and project each contour to the horizontal line of the same elevation. Make a dot at this location f. Connect the dots. g. Round out hills and valleys- do not draw lines straight across
Place a paper strip over the line you want to draw a profile of. Mark clearly each line of contour of your line. Below these marks, write down the elevation of each line of contour.