Techniques > Navigational Questions & Answers

On Latitude & Longitude: why the confusion?

**MoonMan**:

having read that some are uncertain about how Latitude & Longitude work {something that I was taught in Primary School}, I present this simple explanation: the Earth rotates about its axis, the Axis of Rotation, or Longitude, is also known as the Meridian; the Plane of Rotation, or Latitude, is parallel with the Equator, which is the Null point of N or S, the Poles being at 90 degrees thence. E & W are, by International Agreement, measured from the Greenwich Meridian, formerly Teneriffe, Hamburg, Paris, Beijing, or elsewhere. Grid Reference is only of use if one have a map; Navigational Astronomy gives its results in terms of Degrees, Minutes, & Seconds, Knots are the measure of Seconds of Arc traveled one hour. eg: the square root of height in Feet equals Distance seen in Knots, or Minutes of Arc. A protractor will assist one to visualise what is intended.

**captain paranoia**:

One simple problem I think people have with lat/long is the order in which they're given; up/along. This is the opposite to Cartesian coordinates used in so many other fields and forms, including grid references.

Lat/long certainly has its uses (especially in astronomy...), but for land navigation using linear measures, a linear grid system using a suitable transformation makes life a lot easier.

**MoonMan**:

Cartesian Coordinates have polarity: that is, Above /Below; Left/ Right; Ahead/Behind. That is to say,all values are multiples of the Square Root of Minus One . thus, x2 = w2; x2 + y2=w2; & x2 + y2 + z2 = w2.

This was first noticed by William Rowan Hamilton,of Dublin,who discovered Quaternions.,who used these as products, rather than sums.

On the ground, think of where There is, in relation to Here. The shortest distance is always w.

**Lyle Brotherton**:

For the sake of clarity for all forum members

On land, sea and in air navigation Latitude and Longitude is the universal coordinate system used the world over. All air-traffic and maritime vessels use it, plus many of the emergency services.

For us as land navigators it can be used when we are in regions of the world where there has not been a national grid system established (such as the British National Grid).

For land navigators involved in SAR (Search & Rescue) the understanding of how to take and give Lat/Long coordinates is important, as fixed wing aircraft, as opposed to UK SAR helicopters which use the BNG (British National Grid) use the Lat/Long system and if an area designated to be searched is being conveyed to this type of flight Lat/Long coordinates should be used.

In summary:

Latitude

• All lines of latitude run horizontally around the globe

• lines of latitude run parallel east to west

• used to express how far north or south you are, relative to the equator

• shows your location in a north–south direction

• latitude is an angular measurement in degrees from 0° at the equator (low latitudes) to 90° at the poles (+90° N for the North Pole or --90° S for the South Pole)

• lines of latitude are always the same distance apart – 1° = approx. 110 km

• abbreviated to Lat

• sometimes called parallels.

Longitude• all lines of longitude run vertically on the globe and converge at the poles

• start at True North

• shows your location in an east–west direction

• longitude is given as an angular measurement ranging from 0° at the Prime Meridian (also known as the International Meridian at Greenwich, England) to +180°E and

--180°W

• abbreviated to Long

• sometimes called meridians.

Long/Lat is measured in degrees (°), minutes (') and seconds (").

Where 60” (seconds) = 1’ (minute) and 60’ (minutes) = 1° (degree).

**MoonMan**:

So, I gather that the problem lays in whether one think in Grid or Polar Coordinates: grids exist only on maps & street plans, they nominate a square by its edges. In the real world, as opposed to a nominal one, one uses the Earth's axis as a reference, there is nothing "imaginary" about it, it is only invisible. The Latitude, Longitude, & Altitude assume that the Earth is a perfect sphere, for the purposes of applied mathematics, termed Geocentric. & is Nominal. This is further adapted to take in the reality of an Oblate Spheroid, termed Topocentric, & is much close to the Real.

The difference is that the exact location, in the cross-hairs of lat. & long.,rather than pigeon-holed in a box.

Consider: one does not travel along horizontal grid line A till he reach vertical grid line B, but finds the direct route: A2+B2=D2. Likewise, the angle arc sine B/D is the outward Course, the angle arc sine A/D is the return Course. It matters not that one ascertain the Course Angle by Grid or by latitude & Longitude, the result will be about the same. The Earth is not flat: maps are. One needs to be able to imagine his place in Space-Time, & refer his map to that, not vice versa. The real map is in one's Noticing & Recollecting the surroundings, the nominal map is on paper or in a computer programme. Very handy to study before going, but inattention to surroundings can lead to one being misled by the map.

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