Drawing Isolines
Aim: What do isolines represent?
Objectives
Draw isolines accurately on a field map
Interpret field map data by reading isolines
Calculate the gradient on an isoline field map
Draw a profile of an isoline map
Vocabulary:
Isoline
A line connecting points of equal value.
Isotherm:
A line connecting points of equal temperature
Isobar:
A line connecting points of equal barometric (air) pressure
Contour:
A line connecting points of equal altitude
Anything else you can get a value for.
Vocabulary:
Interval
The value from one line to the next
Profile
The side view represented by the isoline map
Gradient
The rate at which the values change on the map
Field value
What is represented by the map
( i.e. temperature, air pressure, altitude, air quality, etc.)
Rules for Drawing
Isolines:
1. Isolines connect points of
equal value.
5
5
10
10
10
10
15
15
2. Isolines are gentle, curving
lines- no sharp corners.
5
5
10
10
10
10
15
15
3. Isolines are always closed
curves even though the map
might only show part of it.
4. Isolines NEVER cross.- This
would mean that one point
has two different values. Ex:
one spot has two temperatures?
40 °
50 °
30 °
60 °
X
20°
Y
Z
5. Isolines usually are parallel.
(They have a parallel trend.)
Highlight
data
points.
Isoline Practice #1
Fill in
gaps in
data.
Connect
the dots.
Go on
to the
next
value.
Isoline Practice #2
Isoline Practice #3
Gradient
Gradient shows how quickly the value
changes from one point to another.
Pg 1 of the ESRT – FIND
Gradient 
 value
dis t anc e
Example #1
Field Value = temperature = Isotherms
The front of the room is 25oC and the back of
the room is 20oC. The distance from the front to
back of the room is 10m.
What is the temperature gradient of the room?
Example #3
Field value = air pressure = Isobars
The air pressure in NY is 993 mb and the air
pressure 500 km away in Chicago is 1007 mb.
What is the pressure gradient between these two
cities?
Example #2
Field Value = elevation = Contour lines
The bottom of a mountain is 100 m above seal
level. The top of the mountain is 1500m. The
distance from the bottom to top of the mountain
is 700m.
What is the elevation gradient?
Lab – Temperature Field Map
You need:
Pencils
Rulers
Calculators
How does a steep or gentle gradient look
on a field map?
A steep (high) gradient changes quickly and the
isolines are close together.
A gentle (low) gradient changes slowly and the
lines are far apart.
Steep area
Gentle area
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Isolines