Topic 3b_BB_3SlidesPerPage

Topic 3b_BB_3SlidesPerPage - Measurements From Maps...

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1 Measurements From Maps Before taking measurements, ensure that Caution! that: The _______________ is appropriate. Accuracy Standards/Source are known. Appropriate Scale. Map is up-to-date. Map is in good condition (shrinkage, tears). Measurements From Maps (Cont.) Distance Measurements. Scaling - Using the scale to measure distance. Techniques can include engineer’s scale, dividers, or marks on the edge of a piece of paper. Map Measurer - Device to measure distance on the map (inches, cms etc.) and then converted into real world distance. Computer assisted - GIS programs, Arc Info, Arc View. Map Measurer
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2 Measurements From Maps (Cont.) Measuring Area. Direct Methods of Measurements. Scaling and computation –est imated directly if the feature is rectangular or square (city block or a building). Graphic Area Scale – superimposed upon transparent material that may be moved over the map. Polar Planimeter – an instrument used to measure area in square inches or centimeters. 9 16 25 Graphic Area Scale 1 4 Polar Planimeter
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3 Measurements From Maps (Cont.) Measuring Area (Cont.). Indirect Methods of Measurements. Grid Squares Method -method of determining area by overlaying the area of interest with a right angle grid of lines, spaced at an appropriate distance apart, where each cell may represent 1km 2 . Dot Planimeter Method - like Grid Squares but Dots are used for the overlay and the area and calculated. Grid Squares Measurements From Maps (Cont.) Measuring Area (Cont.). Indirect Methods of Measurements. Polygon Method – study area is subdivided by regular geometric shapes. The area of these shapes is then calculated and summed. Computer Assisted Methods – GIS packages: Most popular and the easiest, computer will employ a method as described above.
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4 Polygon Method USGS Topographic (Topo.) Maps Obtained from the United States Geologic Survey (USGS). Quarter Million Series 1:250 000 Quarter Million Series 1:250,000.
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Topic 3b_BB_3SlidesPerPage - Measurements From Maps...

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