Session 3
Measuring
Latitude and
Longitude
We are located
West of the
Prime
meridian and
North of the
Equator.
L
A
T
I
T
U
D
E
S
C
A
L
E
090 N
Latitude
is
measured
from
zero
One
minute
of
latitude
The latitude
degrees at the equator to 90
scales
are
is
equal
to poles.
one
degrees
at
the
found
at the
nautical
mile.
In our area, the latitude scale,
000
left
and
at the
right
or right
left-hand margin,
The
latitude
scales
margins
ofthe
a bottom of
increases
from
can
becharts
used
to the
our nautical
toward
chart.
measuretop.
distance.
090 S
L
A
T
I
T
U
D
E
S
C
A
L
E
LONGITUDE SCALE
Longitude is measured from
The
Longitude
zero at the prime meridian in
Greenwich,Scales
UK, eastare
and west
to a pointlocated
in the Pacific
Ocean.
at the
top
and scale,
In our area, the
longitude
at the topbottom
or bottom
ofmargin,
a
increases
from right
to left
nautical
chart..
LONGITUDE SCALE
General Rules
On a chart, LAT/LON is read in:
 Degrees
 Minutes
 Seconds
Set your GPS to read out in this
LAT/LON expression.
LAT/LON Expressions
On a Nautical Chart:

042 deg 56 min 45 sec North

072 deg 45 min 25 sec West
Typical GPS or LORAN read out:
 042 56.750 N
 072 45.417 W
Rules for reading LAT/LON
On a Nautical Chart:
Read the Degrees from the
LAT/LON scales.
 Read the Minutes from the
LAT/LON scales.


Measure the Seconds.
Finding Your Latitude Position
Latitude Scale
Longitude Scale
SMALL SCALE CHART
W Or ‘A’
Fl 4sec BELL
Measuring the Seconds of Latitude.
Step ONE – Place one point of the dividers on the
object or target.
Step TWO - Stretch the other point of the dividers to
nearest Parallel of Latitude.
Step THREE Without disturbing
the opening, move
the dividers to the
Latitude scale in the
left or right margins.
2
3
Step FOUR - Read
the seconds of
latitude.
4
1
The
LATITUDE
SCALE
on
a
The LATITUDE Scale
Small Scale Chart usually
The
parallel decimal minutes.
depicts
line from
the Bell.
041 10.7” N
11.0 min.
Seconds
041 10’ 42” N
10.5 min
Degrees
10.0 min.
Minutes
DISTANCE
One Minute of
Latitude
equals
One Nautical Mile
DISTANCE
Sixty Seconds of
Latitude
equals
One Nautical Mile
The Second Scale on a Small Scale Chart
1/10 of a Mile
ONE
NAUTICAL
MILE
6 seconds
SIXTY
SECONDS
OF
LATITUDE
Finding your Longitude Position
Latitude Scale
Longitude Scale
SMALL SCALE CHART
W Or ‘A’
Fl 4sec BELL
Measuring the Seconds of Longitude
Step ONE - Place one divider point on the object or
target..
Step TWO - Stretch the
other point of the dividers
back to the nearest
meridian of Longitude.
2
Step THREE - Without
disturbing the opening,
move the dividers to the
Longitude Scale at the top
or bottom margin.
1
3
Step FOUR - Read the
seconds of Longitude.
4
The Longitude Scale
The vertical line
from the Bell.
Seconds
Minutes
071 01.4’ W or 071 01’ 24” W
Degrees
Any questions about
how to read and plot
Latitude and Longitude?