Lab Exam - Topographic Maps Topographic Map o Represents...

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Topographic Maps Topographic Map o Represents reduced views of the earth’s surface. Show size, shape and interrelations of geomorphic features. Scales – measures amount of reduction o Verbal scale – a specific distance on a map is equal to a specific distance on the ground o Graphic scale – calibrated bars or lines o Fractional scale – fixed ratio between distance measured on a map and an equal distance measured on the earth’s surface Latitude o Angular distance between earth’s equator and a parallel of latitude passing through a specified point o Measured along the meridian – line connecting poles o 1 ° = 60’ minutes o 1’ minute = 60’’ seconds Longitude o Defined along any meridian which is perpendicular to the equator o Angular distance east or west of the prime meridian (passes through royal Greenwich observatory in UK) Contour Lines o Connect points of equal elevation o Different contour lines do not cross o Spacing of contour lines is relative to ‘steepness’ of slope Widely spaced = gentle slope Closely spaced = steep slopes o Contour liens which cross stream valleys form V’s which point upstream o Contour Interval – vertical distance of separation between adjacent contour liens (CI) Elevation o Vertical distance of a point above seal level o Same as altitude o Bench mark – survey locations o Local relief – difference in elevation between two nearby topographic features o Maximum relief – difference in elevation between the highest and lowest points within an area of the map o Height – difference in elevation between an elevated topographic feature and its immediately adjacent base Gradients = slope
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o Change in vertical height over change in horizontal length o Gradient = difference in elevation/horizontal separation on map Two elevations 182’ and 118’ are separated by distance of 1.8 on map Gradient = 182-118 / 1.8 = 35 ft/mi o Average gradient of a stream = change in elevation / total length of channel between two contour lines Vertical Exaggeration o Emphasize topographic variations o Produced by using a vertical grid with a larger scale than that of the map o Vertical Exaggeration = vertical grid scale / map scale Vertical grid of 1in=100ft 1:1,200 and map scale is 1:62,500 VE = (1/1200) / (1/62500) = 62500/1200 = 52X Vertical distances on profile are magnified 52 times of actual area Conversations 1 ft 12 in 1 mi 5,280 ft 1 mi 63,360 in 1 in 2.52 cm 1 m 100 cm 1 km 100,000 cm Magnetic Declination o Angle between magnetic north and true north o Positive east of true north and negative west of true north o Changes over time and with location
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Stream Erosion and Deposition o Map has a scale of 1:60,000 and map is 12 inches wide, how many miles does your map cover left to right?
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