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 5th 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