Lab 1: Map Coordinate Systems and Map Reading

Transcription

1 Lab 1: Map Coordinates Systems and Map Reading Table of Contents 1. Purpose: Specific learning objectives: Materials: References: Latitude and Longitude, UTM, State Plane General Land Office (GLO) system LAB 1 Exercises: (Print and turn in from this page forward) Purpose: To gain knowledge of the information provided on standard USGS topographic maps and develop competence in using the maps for determining distances, interpreting terrain, and for establishing locational coordinates. 2. Specific learning objectives: Understand what information is given in the margin of the map; Know how to convert map distances to ground distances and vice versa; Know what colors and symbols are conventionally used on maps; Understand the fundamentals of the General Land Office survey system; Be able to visualize the shapes of terrain features after inspection of map contours; Be able to calculate slope from map contours. 3. Materials: Moscow Mountain quadrangle-7.5 minute series (topographic map, provided); ruler; graph paper (provided in lab); Aerial Photo Scale Protractor (provided in lab) When this lab is due: Lab1 is due in exactly one week. Labs are typically due at the end of your lab section for the following week. Section 1: Lab 1 is due 3:20pm, on Tuesday, January 26 th. Section 2: Lab 1 is due 3:20pm, on Thursday, January 28 th. Section 3: Lab 1 is due 5:20pm, on Thursday, January 28 th. 1 updated ES ver2

2 4. References: Bolstad (2012): Chapter 3 Geodesy, Datums, Map Projections, and Coordinate Systems - Web site: Nationalmap.gov 5. Latitude and Longitude, UTM, State Plane Map coordinate systems are crucial for natural resource information (such as range allotments, forest stand inventory information, recreation boundaries, wildlife and fisheries information, etc.) to be usable in a computerized geographic information system. All land management agencies are implementing geographic information systems at local, regional, national and global levels. A prerequisite for managing spatial/geographic information is the development and use of map projections and map coordinate systems for referencing all information acquired on the ground and/or via any type of remotely sensed data acquisition. You should be able to calculate this yourself, but the geographic coordinate dimension for our Moscow Mountain map (these numbers will differ for different latitude and longitude positions) is: Latitude = 7.8 seconds per map centimeter (1cm = 7.8 seconds latitude) Longitude = seconds per map centimeter (1cm = seconds of longitude) The dimensions for the State Plane Coordinate System (SPCS) and the Universal Transverse Mercator (UTM) are: SPCS: 10,000 feet = 5 map inches or map millimeters (or 1 =2,000 ft.) UTM: 1,000 meters = 1.64 map inches or 41.6 map millimeters (or 1 = m) 2 updated ES ver2

3 Lab 1: Map Coordinates Systems and Map Reading 6. General Land Office (GLO) system Much of the land in the western United States has been surveyed using the General Land Office (GLO) System, as authorized by Congress in 1785 under the U.S. Public Lands Survey. It is still used by the Forest Service, Bureau of Land Management, Surveyors and County Assessors to identify ownership. This system is schematically represented below: Because the land tenure system is based upon GLO survey lines, a highly recognizable square grid pattern is often present in aerial photographs, especially those taken over cultivated land. The pattern can help you determine direction and scale quickly and conveniently. Unfortunately for metric enthusiasts, the survey system is based upon Gunter's chain, a unit of measurement 66 feet long (4 rods), divided into inch "links". The convenient thing about the chain is that 80 of them make a 5280-foot mile. A section is 3 updated ES ver2

4 nominally 80 ch (= 1 mile) on a side. A quarter-section is 40 ch (= ½ mile) on a side. A quarter-quarter section is 20 ch (= ¼ mile) on a side. A section contains 640 acres, a quarter- section 160 acres, and a quarter-quarter section 40 acres--which is why it's called a "forty". Sections are grouped into townships 6 miles on a side, and the 36 sections in a township are numbered in the eccentric fashion illustrated above. Take a look at your topographic map. Note Section 6 in the lower right corner in the NW extremity of Township 39 North, Range 3 West; the marginal information tells you what township and range you're in. Notice that the few section lines that have been officially surveyed (solid lines) tend to be in the non-forested parts. Map Units and Scale Each side of the map is 7.5 minutes of latitude or longitude in length. Latitude and longitude are given at each corner of the map. Such maps, at a scale of 1:24,000 (as given on bottom center margin), are the current standard product of the U.S. Geological Survey, the chief civilian mapping agency of the United States. Formerly, 15x15-minute maps at a 1:62,500 scale were standard, but these are no longer available. The 15' maps cover four times the area of the 7½' maps, even though they are physically smaller. The scale of the map is 1:24,000. When a scale is presented this way--as a unitless ratio or fraction with a numerator of 1--it is termed a "representative fraction." It may also be written as 1/24,000. It means, "one unit of distance on this map represents 24,000 of the same units on the ground." For non-technical purposes it is often convenient to express map scale as a "unit equivalent"--in terms of two different units of measure, one of which is understood to apply to map measurements, the other to ground distances. A road map, for example, might bear the legend, "1 inch = 1 mile". Maps made to the 1:24,000 scale are frequently referred to as "2½ inch to the mile" maps. Map Colors and Symbols USGS maps are printed in five colors including black. These denote the following: Black: most man-made features and place names Blue: water Brown: elevational contours Green: forested land (approximate only) Red: main roads, built-up areas, U.S. land survey section lines, fence lines Standard map symbols, some of which appear on your map, are given on the sheet "Topographic Map Symbols." On USGS maps the red squares are section lines, nominally a mile on a side. Where surveyed section corners have been found on the ground, section lines are represented by solid red lines with crosses at the corners to denote surveyors' markers. Dashed red lines represent section lines to theoretical corners where there is not enough evidence to ascertain their position. 4 updated ES ver2

5 Lab 1: Map Coordinates Systems and Map Reading TOPOGRAPHIC MAP SYMBOLS (Variations will be found on older maps) 5 updated ES ver2

6 Contour Lines The brown lines on the map are contour lines. Each represents a horizontal "slice" of uniform thickness through the terrain, and connects points of equal elevation. On this map, the contour "slices" are 20 feet thick--each contour line is 20 feet above and below its neighbors. That is the meaning of the statement in the margin, "contour interval 20 feet". Every fifth contour line is more heavily drawn than the others, and is labeled with its elevation in feet above mean (average) sea level. These heavier lines are called "index contours". Contour interval varies from map to map, depending on the nature of the terrain. In flat country, a contour interval of 10 feet might be necessary to depict topography, whereas in steeply mountainous country an interval of 100 feet might be needed to prevent crowding the map with contour lines. Contour lines work like this: 6 updated ES ver2

7 Lab 1: Map Coordinates Systems and Map Reading In planimetric view, contour lines on a regular slope are evenly spaced. On a convex slope they are spaced more widely at the top, where the slope is gradual, than at the bottom, where the slope becomes steeper. On a concave slope they are closer together at the steeper top of the slope, and farther apart near the bottom, where the slope decreases. Contour lines are what distinguish a "topographic" map from a "planimetric" map. The latter shows features such as roads, streams, and boundary lines in true plan position, as does the topo map; but unlike the topo map, the planimetric map does not systematically depict elevational differences. Forest Service ranger-district maps and almost all road maps are planimetric rather than topographic. Close study of this map will teach you much about the peculiarities of the contour-line method of representing topography--that, for example, contour lines in the vicinity of streams form "V's" with their points upstream: Figure 1. USGS contour map showing contour lines in the vicinity of streams that form "V's" with their points upstream. 7 updated ES ver2

8 Slope Slope of terrain is easily determined from a contour map. expressed as a percentage: Slope is ordinarily change in elevation. horizontal distance x 100 = % slope Of course, both horizontal distance and elevational change must be in the same units if this expression is to make sense. Thus, if the ground rises 10 feet for every 100 feet of forward progress (measured horizontally rather than along the slope), the slope is: x 100 = 10% "Slope equals rise over run" is a frequently encountered mnemonic. slope--1 foot of rise for every foot of run. A 10% slope is considered a very severe road grade. 8 updated ES ver2

9 Lab 1: Map Coordinates Systems and Map Reading FOR375 Section #: Student Name: 7. LAB 1 Exercises: (Print and turn in from this page forward) Lay out and inspect your map of Moscow Mountain. 1. On our 7.5 minute topographic map there are four coordinate systems, list these: (4pts.) Using your scale, determine the geographic coordinates of the following locations: (2pts.) The peak of Basalt Hill: Longitude (x): degrees minutes seconds direction Latitude (y): degrees minutes seconds direction The center of the larger pond located at SW 1 /4 SW 1 /4 Sec.25 T40N R4W: Longitude: degrees minutes seconds direction Latitude: degrees minutes seconds direction 9 updated ES ver2

10 3. Using your scale, determine the Universal Transverse Mercator Coordinates of: (2pts.) The peak of Basalt Hill: Easting (x): meters Northing (y): meters The center of the larger pond located at SW 1 /4 SW 1 /4 Sec.25 T40N R4W: Easting: meters Northing: meters 4. Using your scale, determine the Idaho State Plane Coordinates of the peak of Basalt Hill: (1pt) Easting (x): feet Northing (y): feet 10 updated ES ver2

11 Lab 1: Map Coordinates Systems and Map Reading a. General Land Office (GLO) system Exercises Follow the dividing line between R3W and R4W from south to north on the map and observe the many irregularities in the sections that border it. Sections are not always of uniform dimensions; further, their boundary lines do not invariably follow true azimuths. In spite of irregularities, the lines originally surveyed are the present legal boundaries. 5. How many acres are in Section 31, T41N R3W, if 43,560 square feet = 1 acre? acres. (1pt) 6. How many acres are in S6 T40N R3W if the E-W dimension is assumed to be 2.64 on the map? acres. (1pt) 7. Give the complete U.S. Public Lands Survey description down to a 40 ac block for the location of the Village of Troy Reservoir spillway. (1pt) b. Map Units and Scale Exercises 8. Near the middle of your map is section 15. How long is the northern edge of this section square on the map in inches? in cm? (1pt) 9. How long is that line on the ground in inches?, in cm? 11 updated ES ver2

12 10. Convert ground distance to feet:, to meters: Convert ground distance to miles:, to kilometers: (3pts) 11. If you took the topo map for the literal truth, and lay off a 2.50" line on your map, how long would it actually be on the ground, in feet?, in meters? (1pt) 12. What is the correct number of map inches per mile for a 1:24,000 scale map?, cm per km? (1pt) The accuracy of maps like these is controlled by National Map Accuracy Standard requirements. The standards specify that 90 percent of "all well-defined features" will be within.02 inch--on the map--of their actual positions. 13. How many feet are represented by.02 inch at 1:24,000? ft. (1pt) 12 updated ES ver2

13 Lab 1: Map Coordinates Systems and Map Reading a. Contour Lines Questions 14. To gain an understanding of what contour lines show, make a north-south terrain profile of Moscow Mountain on graph paper: (5pts) 1. On your map, draw a true N-S line through the benchmark on the summit of the mountain, extending exactly 5" N and S of the benchmark. (10" line in total) 2. Take a piece of graph paper, fold it lengthwise along one of its principal graduations, and lay it along side this 10" line. 3. At every index contour make a tick mark on the graph paper and write down the elevation. The horizontal scale of your graph will be the same as that of the map: 1:24,000, or 1"=2,000'. 4. Exaggerate the vertical scale by making it 1"=1,000' (a 2X exaggeration of the vertical) and trace out the terrain profile with a row of dots. Each time you come to a tick mark indicating a change in elevation, go up or down 0.1". 5. Then connect the dots with a smooth curve. Repeat the process without vertical exaggeration on the same profile graph: i.e., go up or down only 0.05" for each 100' change in elevation. So your final graph should have two plots of the elevation profile. On the left Y-axis show the scale at 1 =2,000, on the right Y-axis show the scale at 1 =1,000. Left Y- axis Right Y- axis 15. The National Map Accuracy Standards require that 90 percent of all contours be accurate within half the contour interval. The cartographer who made your map thus had to work within a tolerance of + feet. (1pt) 16. What is the slope of the first 1000' of road running NW from East Moscow Mtn (4721)? Measure off 1000' of ground distance and count the contour lines to find the elevation change. Slope = %. (1pt) 17. What is the general shape and the average percent slope of the terrain running 500' south from the Moscow Mtn. VABM? Shape Slope %. (1pt) 13 updated ES ver2

14 b. Slope Exercises (show compete work, including formulas, to get credit) 18. Given: Vertical distance v = 10 ; horizontal distance (h) = 150 Question: What is the slope? (1pt) 19. Given: v = 10m; Slope (S) = 6% Question: What is the horizontal distance in meters? (1pt) 20. Given: h = 1150 ; S = 7% Question: What is the v in feet? (1pt) 21. Provide a brief (one paragraph) write-up of what you learned in this lab exercise. (1pt) 14 updated ES ver2