Topographic MapsReading Contour Maps
Topographic maps show the shape of the landBy the shape of the contour lines on the map
How do you read this map?
Rules for Reading a Topo Map:circles=hills or mountains
close lines=steep slope (cliff=escarpment)
far apart lines=flat or gentle slope
stream flow=contour lines bend upstream (rule of v’s)
The higher the elevation, the smaller the circle in a series of closed contour lines
Lets practice reading one…
The highest and lowest point
The highest point or elevation on a contour map is equal to the highest possible elevation -1 (without going to the next contour line)
The lowest point or maximum depth is found in a depression. This is indicated by hachured contour lines. This is equal to the depth of the depression -1. The minimum depth will always be the value of the depression -1.
Profiles and gradient
A profile is a cross sectional view of the land or a side view. We can easily create a profile.
The gradient of the land refers to the steepness of the land. The formula is on page 1 of the ESRT.
Other important features:• Magnetic Declination: is given at the
bottom of the map usually.
• Magnetic declination, sometimes called magnetic variation, is the angle between magnetic north and true north.
• Magnetic declination changes over time and with location.
• http://www.ngdc.noaa.gov/geomag-web/#declination
Magnetic Declination
Map Scale
1 inch=2,000ft
Finding Gradient
• Use formula: Gradient = change in Field Value/Distance
• Unit: for exampe… field value unit/meter or field value/mile
• Lets try a problem
Creating a Profile
• Sum Up
• 1. Mark Contour Lines
• 2. Line up Paper and Mark contours lines, label with elevation
• 3. Line up scrap paper with grid. Move paper up and down to plot points.
• 4. Connect points with a smooth line/curve as directed