1. Session 3 Measuring Latitude and Longitude

2. We are located West of the Prime meridian and North of the Equator.

3. One minute of latitude is equal to one nautical mile.
SCALE
090 N
LATITUDE
SCALE
Latitude is measured from zero degrees at the equator to 90 degrees at the poles.
In our area, the latitude scale, at the right or left-hand margin, increases from the bottom of our nautical charts toward the top.
One minute of latitude is equal to one nautical mile.
The latitude scales can be used to measure distance.
The latitude scales are found at the left and right margins of a chart.
000
090 S

4. LONGITUDE SCALE
Longitude is measured from zero at the prime meridian in Greenwich, UK, east and west to a point in the Pacific Ocean.
In our area, the longitude scale, at the top or bottom margin, increases from right to left
The Longitude Scales are located at the top and bottom of a nautical chart..
LONGITUDE SCALE

5. General Rules On a chart, LAT/LON is read in: Degrees Minutes Seconds
Set your GPS to read out in this LAT/LON expression.

6. 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: N W

7. 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.

8. Finding Your Latitude Position
Longitude Scale
Latitude Scale
SMALL SCALE CHART
Students should break out their charts and dividers to
follow along
Latitude goes up the side divided in one tenth of minute
Longitude goes along the top and bottom
Locate the White and Orange buoy “A” in the bottom left quadrant
W Or ‘A’
Fl 4sec BELL

9. 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
Spread dividers and put one point on object
The nearest line is 41° 20’N
You want to insure it is just touching the line
Read off the longitude at the bottom
Answer 3
Step FOUR - Read the seconds of latitude. 4 1

10. The LATITUDE SCALE on a Small Scale Chart usually depicts decimal minutes.
The parallel line from the Bell.
11.0 min.
” N
Seconds
041 10’ 42” N
10.5 min
Degrees
10.0 min.
Minutes

11. One Minute of Latitude equals One Nautical Mile
DISTANCE
One Minute of
Latitude
equals
One Nautical Mile

12. Sixty Seconds of Latitude equals One Nautical Mile
DISTANCE
Sixty Seconds of
Latitude
equals
One Nautical Mile

13. 6 seconds 1/10 of a Mile ONE NAUTICAL MILE
The Second Scale on a Small Scale Chart
6 seconds
1/10 of a Mile
SIXTY
SECONDS OF
LATITUDE
ONE
NAUTICAL
MILE

14. Finding your Longitude Position
Longitude Scale
Latitude Scale
SMALL SCALE CHART
Students should break out their charts and dividers to
follow along
Latitude goes up the side divided in one tenth of minute
Longitude goes along the top and bottom
Locate the White and Orange buoy “A” in the bottom left quadrant
W Or ‘A’
Fl 4sec BELL

15. 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.
Spread dividers and put one point on object
The nearest line is 071° 20’W
You want to insure it is just touching the line
Read off the longitude at the bottom
Answer 1 3
Step FOUR - Read the seconds of Longitude. 4

16. The vertical line from the Bell.
The Longitude Scale
The vertical line from the Bell.
Seconds
Degrees
Minutes
’ W or ’ 24” W

17. Any questions about how to read and plot Latitude and Longitude?