Coordinate System Unit 1: Mapping the Earth

1. Coordinate SystemUnit 1: Mapping the Earth This unit is comprised of two main concepts; our coordinate system based on latitude and longitude, and using topographic maps that indicate landforms and human construction. Concept 1: Our coordinate system Big Ideas: see NYS standards for mapping. Key Idea 1: 1.1c and 1.1d and 1.1f.

2. 1. Our planet is a rotating sphere. Drawn to scale, it is perfectly round. In truth, the equatorial diameter is greater than the polar diameter.

3. 2. Latitude gives locations in degrees north and south of the equator. There are 90 degrees from the equator to the North Pole and from the equator to the South Pole.

4. a.     Temperatures change with latitude. The solar noon angle of the sun’s rays decreases towards the Poles, because earth is a sphere.

5. b.     Polaris is visible only in the Northern Hemisphere. The altitude of Polaris equals the observer’s latitude in the Northern Hemisphere.

6. c.      Each degree of latitude equals approximately 112 km or 70 miles. • d.     Lines of latitude run parallel to the equator and are called ‘parallels’.

7. e.     New York State’s latitude is between 400 and 450 North latitude. As seen on page 3 of ESRT, the degrees of latitude are each divided into 60’. • http://www.emsc.nysed.gov/osa/reftable/home.html links to the reference tables

8. 3. Longitude gives locations in degrees east and west of the Prime Meridian (PM) to the International Date Line (IDL). • a.     The Prime Meridian is an arbitrary line with a value of 00. The IDL is 1800 from it.

9. b.     There are 1800 East of the PM and 1800 West of the PM. The date changes at the IDL. • c.      Lines of longitude are called meridians, and come closer together at the Poles. There is no set distance between lines of longitude.

10. d.     Time changes with longitude because the earth is rotating at a rate of 150/hr. • e.     There are 24 time zones of 15 degrees longitude each. Due to earth’s rotation from west to east, locations East of an observer are later and locations West are earlier.

11. f.       New York State longitudes are between 720W and almost 800W.

12. 4. Coordinates: Earth’s coordinate system is really a graph or grid. • a.     The coordinates of any location on earth are the latitude and longitude. • b.     The coordinates must include direction. Montgomery, NY is 41030’N, 740 05’W.

13. 5. Mapping the Earth: Because the earth is round, all flat maps will have distortions of shape and distance.

14. a.     Page 3 of ESRT is a map of NYS that includes latitude and longitude, and is precise to minutes of each degree. • b.     Page 4 and 5 are Mercator projections of the world.  Mercator is the most accurate for direction. • d.     Improvements in technology allow mapmakers to use satellites, lasers and computers to pinpoint areas on earth accurately and precisely and to identify changes in earth’s surface.

15. Concept 2: Contour maps and topographic maps • Big Idea: From NYS Standards for Earth Science: • Key Idea 2: • Many of the phenomena that we observe on Earth involve interactions among components of air, water, and land. • 2.1q Topographic maps represent landforms through the use of contour lines that are isolines connecting points of equal elevation. Gradients and profiles can be determined from changes in elevation over a given distance.

16. 1. Field maps are localized maps that show one aspect of the area using isolines and symbols. In Earth Science, field maps are used to show elevation, weather variables, pollutants, earthquake intensity, etc.

17. 2. Guidelines for using maps with any type of isolines: • a.     Isolines are lines that connect points of equal value on a field map. • b.     All points on an isoline have the same value as every other point on the isoline. • c.     Isolines must either form a closed loop or begin and end off the map. • d.     Isolines can never cross each other.

18. Guidelines continued • e.     The value change from one isoline to the next is constant, although the distance between them may change. • f.        A map scale is used to measure distance on the map. • g.     A map legend or key identifies the meaning of symbols on a map. • h.      Isolines that are close together indicate a rapid change in field conditions (gradient). • i.         Relief indicates the change on the map from greatest to least field value.

19. 3. Contour Maps: field maps that show elevation. • a.     Contour maps use contour lines (isolines) to indicate landscape changes. • b.     The contour interval between the isolines must always be constant, and is usually measured in feet or meters. • c.     Contour lines spaced far apart indicate flat land. Those close together indicate steep ground.

20. continued • d.     Closed loops indicate hills. Long closed loops indicate ridges. • e.     The maximum possible elevation inside a closed loop is one less than whatever another contour line would be. • f.        Depressions (or basins) are shown using hachure lines. The first hachure line has the same value as the last contour line.

21. g.     The direction a river flows can be interpreted two ways on a contour map: •     i.      The contour lines make a ‘v’ shape that points uphill. •   ii.      The elevation indicates which way downhill is along the river. • h.      Sea level always has an elevation of 0. Elevations below sea level are indicated by negative numbers.

22. 4. Finding gradient: gradient is the change in field value between two points on the map divided by the distance between the two points. • a.     On a contour map, the gradient indicates the change in elevation (y value) and the distance indicates the x value. • b.     The equation for gradient is on page 1 of ESRT: gradient = change in field value /distance • c.     Units are very important in gradient problems. For contour maps, the gradient units will usually be meters/kilometers (m/km) or feet/miles (ft/mi) • d.     To calculate gradient, you must first find the elevations of the two points and then measure the distance between them.

23. 5. Making a profile: a profile uses the contour lines of a flat map to show a side view of a cross-section with elevation. • a.     The steps to making a profile require visuals and practice: • http://user.gs.rmit.edu.au/caa/topo/contours.htm • http://rst.gsfc.nasa.gov/Sect11/Sect11_2.html • Vertical exaggeration refers to how much the elevation has been exaggerated on the ‘y’ axis to make the change visible over horizontal distance:

24. 6. Topographic Maps: contour maps that use a coordinate system, map scale and key and symbols to indicate landforms and manmade structures. • a.     Technology has greatly improved topographic maps. • b.     In the United States, the United States Geologic Survey (USGS) has made USGS Quadrant maps of the entire country. • c.     The USGS Quadrant maps use coordinate systems, including latitude and longitude, to indicate the map location in the world. • d.     Symbols used on these maps are standardized to show vegetation, types of structures, roads, etc. • e.     Topographic maps are used for planning and to track problems and changes.