Concept 2: Contour maps and topographic maps Read: don’t write this part…….. 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.

Field Maps 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.)

2. Map keys and symbols: a. A map scale is used to measure distance on the map. b.     A map legend or key identifies the meaning of symbols on a map. c.    Relief indicates the change on the map from greatest to least field value.

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.

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.

i. The contour lines make a ‘v’ shape that points uphill. 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.      elevation indicates which way is downhill h.      Sea level always has an elevation of 0. Elevations below sea level are indicated by negative numbers. http://www.visualentities.com/contour.htm http://www.sir-ray.com/Topographic%20Map%20Lab.htm

4. Finding gradient: see p. 1ESRT a.     On a contour map, the gradient indicates the change in elevation (y value) over the distance (x value). b.     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)

5. profile maps use the contour lines of a flat map to show a side view of a cross-section 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:

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.