Lab five us geological survey topographic maps & us public


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Lab five us geological survey topographic maps & us public

  1. 1. US Geological Survey Topographic Maps & US Public Land Survey System
  2. 2. Topographic Maps <ul><li>Topographic maps are large-scale maps that use contour lines to portray the elevation and shape of the topography. </li></ul>
  3. 3. Topographic Maps <ul><li>Topographic maps show and name both natural and human-made features. </li></ul>
  4. 4. Topographic Maps <ul><li>The US Geological Survey (USGS) is the principle government agency that provides topographic maps for the United States. </li></ul>
  5. 5. Topographic Maps <ul><ul><li>USGS topographic maps cover the entire United States at several different scales. </li></ul></ul>
  6. 6. Topographic Maps <ul><li>The largest scale maps are those at a scale of 1:24,000 </li></ul><ul><ul><li>1 inch represents 2000 feet and one centimeter represents about 0.24 km </li></ul></ul>
  7. 7. Topographic Maps <ul><li>USGS used to use maps at a scale of 1:62,500 </li></ul><ul><ul><li>1 inch represents about 1 mile and 1 cm represents about 0.6 km </li></ul></ul>
  8. 8. Topographic Maps <ul><li>Those maps have been replaced by 1:100,000 scale maps </li></ul><ul><ul><li>1 inch represents about 1.6 miles and 1 cm represents 1 km </li></ul></ul>
  9. 9. Topographic Maps <ul><li>The entire country is also mapped at a scale of 1:250,000 </li></ul><ul><ul><li>1 inch represents about 4 miles and 1 cm represents 2.5 km </li></ul></ul>
  10. 10. Topographic Maps <ul><li>The primary scale for mapping Alaska remains at 1:63,360. Eventually the entire area will be mapped at a larger scale. </li></ul><ul><ul><li>The scale of 1:63,360 maps is 1 inch represents 1 mile and 1 cm represents .63 km </li></ul></ul>
  11. 11. Scale Categories <ul><li>Map scales are grouped into small, medium and large categories. </li></ul><ul><li>Large scale maps , such as 1:24000 scale maps show a smaller area in great detail. </li></ul><ul><ul><li>They are useful for showing the locations of buildings and other features important to engineers and planners. </li></ul></ul><ul><li>Medium scale maps , (1:62500) are good for agricultural planning where less detail is required. </li></ul><ul><li>Small scale maps have the least detail but show large areas. These are useful for extensive projects at regional levels of analysis. </li></ul>Scale 1:24000 1 inch = 2000feet Area Shown: 1 sq mi Scale 1:62500 1 inch = nearly 1 mile Area Shown: 6 3/4 sq mi Scale 1:250,000 1 inch = nearly 4 miles Area Shown: 107 sq mi
  12. 12. Marginal Data on USGS Maps <ul><li>This exercise focuses primarily on the information found in the margins of topographic maps. </li></ul><ul><li>See figure one. </li></ul><ul><ul><li>This shows the lower right corner of a USGS topographic map with a scale of 1:24,000. </li></ul></ul><ul><ul><li>These 1:24,000 scale maps are also referred to as 7 ½ minute maps </li></ul></ul>
  13. 13. Greasewood Springs, AZ Map <ul><li>The name, or quadrangle , of the map in figure one is “Greasewood Springs, Arizona. </li></ul><ul><li>Below the name is the date of publication, 1972 in this case. </li></ul><ul><li>If any revisions have been made to the map, the date of those revisions would be listed here as well. </li></ul><ul><li>To the left of the name, is a small map showing the quadrangle location in Arizona. </li></ul>
  14. 14. Marginal Data on USGS Maps <ul><li>The latitude and longitude are printed at each corner of the quadrangle. </li></ul><ul><li>The coordinates of the lower right (southeast) corner of this map are 35°22’30” N latitude , 109°52’30”W longitude. </li></ul>
  15. 15. Marginal Data on USGS Maps <ul><li>The eight adjacent quadrangles are named in parentheses around the margins of the map. </li></ul><ul><li>The quadrangle to the southeast of Greasewood Springs is called “Betty Well.” </li></ul><ul><li>In some cases, the eight adjacent quadrangles are shown with a small diagram at the bottom of the map. </li></ul>
  16. 16. Marginal Data on USGS Maps <ul><li>The scales are shown with a small diagram at the bottom center of the map. </li></ul><ul><li>Below the fractional scale (1:24,000), three graphic scales are shown-miles, feet, and kilometers. </li></ul><ul><li>Note “0” is not at the far left edge of the graphic scales. </li></ul><ul><ul><li>This is to make fractions and small distances easier to read. </li></ul></ul><ul><li>Below the scales the contour interval is given. </li></ul><ul><li>The datum is the reference point from which elevations are measured. </li></ul><ul><ul><li>On USGS topographic maps the datum is normally mean sea level. </li></ul></ul>
  17. 17. Marginal Data on USGS Maps <ul><li>The declination arrow is found at the lower left corner of the map. </li></ul><ul><li>True north is shown with the tallest arrow labeled with either a star or a large “N.” </li></ul><ul><li>The “MN” arrow shows the direction of magnetic north . </li></ul><ul><ul><li>The location of the north magnetic pole is not the same as the true geographic North Pole, so it is necessary to adjust for this difference when using a magnetic compass. </li></ul></ul><ul><ul><li>The position of the north magnetic pole changes with time, so the compass correction indicated on the map may not be exact some years after the original survey. </li></ul></ul>
  18. 18. <ul><li>The “GN” arrow shows grid north . </li></ul><ul><ul><li>In addition to the grid system of longitude and latitude, other kinds of grids are also marked on many topographic maps. </li></ul></ul><ul><ul><li>Grid North refers to the orientation of the Universal Transverse Mercator grid (UTM) used by the military. </li></ul></ul><ul><ul><li>Abbreviated numbers for the UTM grid are marked every1000 or 10,000 meters around the margins of the map. </li></ul></ul><ul><ul><li>North-south locations are indicated in meters from a standard meridian. </li></ul></ul><ul><ul><li>Similar state grids are often marked every 1000 or 10,000 feet. </li></ul></ul>The Universal Transverse Mercator grid that covers the conterminous 48 United States comprises 10 zones—from Zone 10 on the west coast through Zone 19 in New England.
  19. 19. Topographic Maps Symbols <ul><li>Standard symbols and colors are used on USGS topographic maps. </li></ul><ul><ul><li>Brown lines are elevation contours. </li></ul></ul><ul><ul><li>Spot elevations are shown by black numbers next to an “X” </li></ul></ul><ul><ul><li>More precisely surveyed points are known as benchmarks and are shown as numbers next to the letters “BM.” </li></ul></ul><ul><ul><li>Blue lines and numbers are used to indicate water features. </li></ul></ul><ul><ul><li>Green is used for various kinds of vegetation or forest cover. </li></ul></ul><ul><ul><li>Human-built features, such as roads, are shown in black and red, and urbanized areas are shown with either red or gray shading. </li></ul></ul><ul><ul><li>Areas that have been photo revised are shown in purple, this means they have been updated with aerial photographs. </li></ul></ul>
  20. 20. US Public Land Survey System <ul><li>The Public Land Survey , or township grid , was established by the federal government in 1785 in order to keep track of land ownership in the American Frontier. </li></ul><ul><li>The grid covers most of the continental United States west of the Mississippi and Ohio Rivers, with the exception of some regions such as those under old Spanish land grants. </li></ul>
  21. 22. US Public Land Survey System <ul><li>The starting point for the grid is a series of parallels known as base lines , and a series of principle meridians . </li></ul><ul><ul><li>See figure 1 </li></ul></ul><ul><li>Beginning at the intersection of a base line and a principal meridian, rows of 36 square-mile tracts of land known as townships were established. </li></ul><ul><ul><li>See figure 2a </li></ul></ul>
  22. 23. Township and Range <ul><li>Each township is a square tract of land, six miles to a side. </li></ul><ul><li>A township is identified by its position north or south of a base line, and east or west of a principal meridian. </li></ul><ul><ul><li>The first position north of a baseline is called “Township 1 North” or T1N, the second position north is T2N, and so on. </li></ul></ul><ul><ul><li>The first position south is T1S. </li></ul></ul>
  23. 24. Township and Range <ul><li>The first position west of a principal meridian is called “Range 1 West” or R1W, and the first position east is R1E. </li></ul><ul><li>Each 36 square-mile township is identified by both a township and a range . </li></ul><ul><li>For example, one of the townships would be designated “Township 3 North, Range 2 East.” </li></ul><ul><ul><li>See figure 2a. </li></ul></ul>
  24. 25. Township/Tier <ul><li>The term “township” has two meanings in the context of the Public Land Survey: </li></ul><ul><ul><li>A 36 square-mile tract of land </li></ul></ul><ul><ul><li>The positions of these tracts north and south of a base line. </li></ul></ul><ul><li>It may help to think of T1N and T2N as referring to “Tier” 1 North and “Tier 2 North, and so on. </li></ul>
  25. 26. Townships <ul><li>A township is divided into 36 sections . </li></ul><ul><li>Each section is one square-mile (640 acres) in area and is given a number from 1-36. </li></ul><ul><ul><li>Notice the specific numbering patterns of sections within a township. </li></ul></ul><ul><ul><ul><li>See figure 2b . </li></ul></ul></ul><ul><li>Each section is subdivided into “quarter sections” (160 acres), and each quarter section is further divided into “quarters of quarter sections (40 acres), or as shown in figure 2c, into even smaller tracts of land. </li></ul>sections
  26. 27. Townships <ul><li>The shaded 10-acre plot shown in figure 2c would be called the “Southeast quarter of the Southwest Quarter of the Northeast Quarter, Section 24, Township 2 South, Range 3 West” </li></ul><ul><li>SE ¼, SW ¼, NE ¼, Sec. 24, T2S, R3W </li></ul>
  27. 28. Township Grid on Topographic Maps <ul><li>On USGS topographic maps, the public land survey grid is usually shown with red lines and section numbers. </li></ul><ul><ul><li>See Map T-11 “Whitewater, Wisconsin,” quadrangle (1 page after Problems). </li></ul></ul><ul><li>The township and range numbers are shown along the margins of the map. </li></ul><ul><li>The base line and principal meridian are often not identified. </li></ul><ul><ul><li>A row of townships is occasionally offset relative to the row to the north or south. </li></ul></ul><ul><ul><ul><li>This is to compensate for the constriction of a township that would result from the convergence of the meridians as latitude increases. </li></ul></ul></ul>