Topographic Maps Fields • Field - any region of space that has some measurable value at every point. • Ex: temperature, air pressure, elevation, wind speed Isolines • Isolines- lines on a map that connect points of equal field value • Isotherms- lines of equal temperature • Isobars- lines of equal air pressure • Contour lines- lines of equal elevation Draw the isolines! (connect points of equal values) Isolines Drawn in Red Isotherm Map Isobar Map Topographic Maps • Topographic map (contour map)- shows the elevation field using contour lines • Elevation - the vertical height above & below sea level Why use sea level as a reference point? Topographic Maps Reading Contour lines Contour interval- the difference in elevation between consecutive contour lines Subtract the difference in value of two nearby contour lines and divide by the number of spaces between the contour lines Elevation – Elevation # spaces between 800- 700 =?? 5 Contour Interval = ??? Rules of Contour Lines • Never intersect, branch or cross • Always close on themselves (making circle) or go off the edge of the map • When crossing a stream, form V’s that point uphill (opposite to water flow) • Concentric circles mean the elevation is increasing toward the top of a hill, unless there are hachures showing a depression • Index contour- thicker, bolder contour lines on contour maps, usually every 5 th line • Benchmark - BMX or X shows where a metal marker is in the ground and labeled with an exact elevation ‘Hills’ & ‘Holes’ A depression on a contour map is shown by contour lines with small marks pointing toward the lowest point of the depression. The first contour line with the depression marks (hachures) and the contour line outside it have the same elevation. 60 hill hole hachures Practice on Your Map Index Contours: red Benchmarks: green Hills: yellow Stream ‘V’: gray (pencil) Stream direction: blue CI: ________ Answers for Your Map Index Contours: red Benchmarks: green Hills: yellow Stream ‘V’: gray (pencil) Stream direction: blue CI: 20 meters Common 3D & 2D Views.