Topographic notes • Topographic Map-includes contour lines drawn to represent changes in elevation. • Topographic maps take 3 dimensional ups and downs of the terrain and show them on 2 dimensional surface. • When reading a topographic map you need to visualize in your minds eye on a 3-D map view of what the symbols and the contour lines are representing.
Topographic Notes • When you follow a path on a topographic map that crosses these contour lines, you will either be climbing or descending. • A path running parallel to contour lines are relatively flat. • The MOST important thing to remember: CLOSE contour lines mean STEEP terrain OPEN contour lines mean FLAT terrain
Contour line and interval • Contour line- lines that connect points of equal elevation. • The red arrows are pointing to the index contour lines. Notice that they are wider than the other lines. • The number in each circle shows the elevation of the index contour lines.
Contour Lines and intervals Rules to reading a topographic map • Where a contour line crosses a stream or valley, the contour line bends to form a “V” that points upstream. In the upstream direction, the successive contours represent higher elevations. • Contour lines near the top of a hill form closed, circular shapes. The top of the hill is higher than the highest closed contour line. • Depressions without outlets are shown by closed hatched contours. The contour lines have short lines on the inside that are pointing downslope. The bottom of the depression is lower than the lowest closed contour line.
Contour lines and intervals • Contour lines are widely spaced on gentle slopes. • Contour lines are closely spaced on steep slopes. • Contour lines DO NOT cross or intersect each other, except in the rare case of an overhanging cliff. • All contour lines eventually will make a closed loop. This closure may be on the map or beyond its margins since contour lines connect features of the same elevation.
Scale and Interval • A scale of 1:24,000 is 1 inch on the map = 24,000 inches on the ground= 2,000 ft or .38 miles. The scale and interval are usually found in the margin of the map.
Benchmark • Benchmark - Accurate measurements of location and the elevation are recorded in the brass and placed on rock or concrete to help surveyors and mapmakers (cartographers) draw maps.
Topographic vs. Satellite • Blue = water features • Green= woodlands, orchards, or other vegetation • Red or grey= urban areas, important roads • Black= man made works, road boundaries (solid or dotted lines) • Brown= Contour lines
Topographic vs. Satellite Satellite images allow map makers and scientists to more easily view and measure the topography of the Earth’s crust. Limitations: They do not show measured changes in elevation.