Latitude and Longitude Home Page
To define a position on the earth’s surface we use Latitude and Longitude.
There are 360 degrees in a circle. Latitude is measured in degrees and minutes North or South of the Equator – the North Pole is 90º North
Longitude is measured in degrees and minutes West or East of Greenwich which is zero degrees, the Prime Meridian.
On the chart below London is approximately 50º N, 000º W. Tasmania is 40ºS, 150º E.
Since a degree of latitude is 60 Nautical Miles (M), we need more precision. Each degree is divided into 60 minutes of arc; one minute of latitude is 1 Mile. Each minute is then divided up to 2 places of decimals.
On RYA Chart 3 look at the bottom right and top left of the chart. The latitude runs from 45º 37’.00 North to 46º 30’.00 North, ie 53 minutes (53 Miles) in total from bottom to top.
Longitude runs from 005º 35’.00 West to 006º 25’.00 West, ie 50 minutes of longitude. (Do not use this for measuring distances).
Gilly Point (Southern Peninsula) is 45º 46’.20 N, 005º 50’.00 W.
The centre of the Compass Rose off Cape Woodward is 46º 07’.20 N, 006º 15’.00 W.
A good exercise is to check the positions of the tidal stream diamonds – the Lat and Long is given above each diamond (A to R) in the table at the top of the chart. The most accurate way is to use dividers, but a ruler will do quite well.Posted Thursday 5th November 2009