3. Chapter 17: Mapping Survey
Control points. Why we need them? Sources.
Horizontal Control: Distance & Direction, or Coordinate, Establish by Traversing, Triangulation, Trilateration, or GNSS Vertical Control: Benchmarks, Establish by Trigonometric leveling with total station or GNSS
Deference between planimetric and topographic maps
The process of determining the positions, on the earth's surface of the natural and man-made features of a given locality and to determine the configuration of the terrain. Planimetric: (x-y) views Topographic: + configuration of the earth's surface
Contour lines, contour internal, index contour
CONTOUR LINES: Most common method to represent the topography of an area is the use of contour lines. Normally every 5th line is bolded. (close lines=steep grade, far= flat grade) A contour line is an imaginary line that connects points of equal elevation. Elevation is estimated from known elevations. CONTOUR INTERVAL: the vertical distance between contour lines, for normal topo maps the contour interval may be between 2 and 20 feet. Flat area every 1/2 foot and mountain areas every 50 to 100 feet. Selection is very important (small enough for the map to serve purpose, are as possible to keep cost down, earthwork = 5ft interval and water storage facilities = 1-2 ft intervals.
Map scales types. Meaning of large scale and small scale maps
The ratio of the length of a feature on a map to the true length of the feature. Equivalence: statement scale/word scale/written - one inch equals four miles Ratio of representative fraction: 1:250,000 or 1/250,000 Graphical: linear/bar scale A topographic map has a contour interval of 1 ft and a scale of 1:600. If two adjacent contours are 0.25 inches apart, what is the average slope of the ground between the contours? Scale=50ft/in H=50(.25)=12.4 ft slope= 1/12.5*100%=8% LARGE SCALE: Objects are relatively larger in size, high details objects, covering the small area, high RF factor (1:24,000; 1:50,000 etc small denominator) SMALL SCALE: Objects are relatively smaller in size, low details objects, covering the large area, small RF factor (1:250,000; etc. large denominator)
