A
From RegentsEarth.com
This is a FIELD. It is simply an area. It can be as large as the universe.............
or smaller than the
period at the end of
this sentence.
In this field or any
field there are things
that can be measured.
We could measure the temperature at different points in the field.
Or we could measure
the amount of rainfall,
or the intensity of
sunlight,
or the volume of a
sound.
There is no end to the
kinds of things that
can be measured as
long as there is some
way to accurately
measure them.
Suppose that we wanted to measure the depth of the snow at various points
in the field. What would we have to do?
First we would have
to send people out
into the field to all
the different places
where we wanted to
take measurements.
Then we would have
to record each
measurement and put
it on a map of the
field.
Remember, we are
recording the depth
of the snow in
centimeters.
SNOW DEPTH MAP
14
13
15
14
16
20
32
25 26
Each value represents
the actual depth of
the snow at that
location in the real
field.
35
23
15
15
17
18
28
20
20
25
35
21
24
26
40
27
25
“Iso” is a prefix
meaning “equal”,
so lines that connect
points of equal value
are called isolines.
36
28
32
38
31
37
43
35
36
40
40
39
42
The next thing we
want to do is to draw
lines connecting
points of equal value.
44
Before we start
drawing we have to
do two things.
SNOW DEPTH MAP
14
13
15
14
16
20
32
25 26
35
23
15
15
17
18
28
20
20
25
35
21
24
26
40
27
25
36
28
32
38
31
37
43
35
36
40
40
39
42
44
First, there are a lot
of numbers and we
may not want to
draw lines for all of
them. If we did the
map might get too
crowded with lines.
Suppose we decide
to draw the isolines
in increments of
5cm.
In other words,
instead of a line for
every value, we only
draw lines for 15, 20,
25, 30, 35, and 40cm
snow depths.
This is called the map
interval. The interval
of this map is 5cm.
SNOW DEPTH MAP
14
13
15
14
16
20
32
25 26
The next thing we have
to do is plan.
Drawing isolines is
a lot like planning a
long road trip.
35
23
15
15
17
18
28
20
20
25
35
21
24
26
40
27
25
First, the 15cm line.
36
28
You just don’t get into
the car and start
driving. First you take
out a map and plan
your route.
Then the 20cm line.
32
38
31
Then the 25cm line.
37
43
35
36
40
40
39
42
44
But now we have a
problem..............
SNOW DEPTH MAP
14
13
15
14
16
20
32
25 26
The interval of the
map is 5cm. So the
next line we should
draw is the 30cm line.
35
23
15
15
17
18
28
20
20
25
35
21
40
This is where planning
comes in!
24
26
27
25
36
28
32
38
31
37
43
35
But there are no 30’s
on the map! How can
we draw the line?
36
40
40
39
42
44
30 is a number
between 28 and 31, so
put a dot between
those two numbers to
represent 30.
30 is a number
between 27 and 32, so
put a dot between
those two numbers to
represent 30.
SNOW DEPTH MAP
14
13
15
14
16
20
32
25 26
35
23
15
15
17
18
28
20
20
25
35
21
24
26
40
That’s because
30 is closer to 28
than it is to 35.
27
25
36
28
32
38
31
37
43
35
36
40
You can’t count from
28 to 35 without going
through 30 so put a
dot between those two
numbers.
But put the
dot a little closer to
the 28.
40
39
42
44
And finally 30 must be
between 26 and 32 so
find those two
numbers and put a
dot there (a little
closer to the 32).
SNOW DEPTH MAP
14
13
15
14
16
20
32
25 26
OK! Now we’re ready
to draw the 30cm
isoline!
35
23
15
15
17
18
28
20
20
25
35
21
24
26
40
27
25
And one more dot
between 32 and 37.
36
28
Now you’re ready to
draw the 35cm line.
32
38
31
37
43
35
36
40
40
39
42
Now plan the 35cm
line.
35 is more than 31
but closer to 36 so
put a dot where you
want your line to go.
44
And finally, draw the
40cm isoline.
SNOW DEPTH MAP
14
13
15
14
16
20
32
25 26
Should we draw a
45cm line?
35
NO!
23
15
15
17
18
28
20
20
25
35
21
24
26
40
27
25
If you can’t be sure,
don’t draw it!
36
28
32
38
31
37
43
35
Why? Because there
are no points with a
value of 45 or greater
so you can’t be sure
where that line would
go.
36
40
40
39
42
44
Also notice that we
have drawn all the
lines from one edge
of the field to the
other. Whenever
possible extend
isolines to the edges
of the map.
Are there times when the isolines don’t extend to the edges of the field?
YES! Look at these
values. They represent
air pressure measured
in units called millibars.
980
980
976
980
The isolines used in
air pressure maps are
called isobars.
976
972
976
972
972
976
972
980
976
976
980
When we connect
points of equal value
the lines form closed
paths.
With practice you
will learn to recognize
isolines that form
closed paths and
others that extend to
the edges.
It’s all about............
980
980
PRACTICE!
A couple of regents-style questions:
What is the value of
point ‘A’?
980
980
976
‘A’ is more than 972
but less than 976. It
is closer to 976 so
point ‘A’ is probably
about.............
980
976
972
972
976
X
976
975
972
972
980
976
976
A
980
980
980
What is the lowest
possible value (to the
nearest whole number)
of point ‘X’?
The map interval is 4.
There is no 968
isoline so X must be
less than 972 but more
than 968. The lowest
value for X is..........
969
980
980
976
980
976
972
976
972
972
980
976
972
976
976
980
What’s wrong with
this line?
It violates an
important rule!
ISOLINES CANNOT
CROSS!
Why? Because if they
crossed, the points
where they intersected
would have 2 values at
the same time!
These points..........
would have a pressure
of 976 and 980 mb at
the same instant and
that’s
IMPOSSIBLE!
One more thing.
When drawing isolines
try NOT to do this.......
980
980
976
In the real world lines
are seldom straight.
980
976
972
So when drawing
isolines don’t use a
ruler.
976
972
972
976
972
980
976
976
980
980
980
Instead use a pencil
(so you can erase) and
sketch the lines lightly.
When you’re happy
with the lines you’ve
drawn, go back and
darken them.
REVIEW
ISOLINE: A line on a
map connecting all
points of equal value
980
980
976
980
INTERVAL: The
numerical distance
between isolines.
976
972
976
972
972
976
972
980
976
976
980
What is the interval
of this map?
The interval is 4mb.
Draw smooth, curved
lines.
Extend the lines to
the edges of the map
or form closed paths
when possible.
Remember.........
Isolines must not
cross!
980
980
BYE!