22. Universal Transverse Mercator (UTM)

Just as we use Latitude and Longitude to locate any place on earth, in a similar way, Universal Transverse Mercator (UTM) is a grid based method to locate any place on the surface of earth in a two-dimensional form.

So what is latitude and longitude ?

Lines of latitude are circular bands running east and west parallel to the equator. They are designated from zero to 90 degrees north and south of the Equator. 

Lines of longitude are circular bands which run north and south through the two poles. They are designated from zero to 180 degrees east and west of the Greenwich Observatory in London, England.  

 In our UTM system, the latitude from 80° S to 84° N is divided into 20 interval. The first 19 interval from 80° S to 72° N are each of 8°while the last one is of 12°, i.e., from 72° N to 84° N.

Starting from the North side towards south, the intervals have been designated with alphabet C to X, excluding the alphabets O and I because of their similarity with the numbers 0 (zero) and 1 (one). 

Now, the longitudes are divided into 60 intervals, each of 6°.

The longitudes form 60 zones designated with numbers 1 to 60.

Thus a UTM grid is formed by the intersection of 60 zones of longitude and 20 zones of latitude.

This is a picture I have taken using Google Earth. Thought it does not indicate all the the zones and their assigned characters but it makes a clear sense about the UTM Grid and Zones.

This is the Top View, i.e., looking towards the North Pole :

This is the Bottom View, i.e., looking towards the South Pole :

Now we can designate any point on earth using UTM coordinate.

To locate any point on the surface of the earth using UTM we use:

a. zone number 

b. its distance in meters from the equator (Northing)

c. its distance in meters from a north - south reference line (Easting)

This is to be noted that the western and eastern sides of the Antarctic region is designated by the characters A and B while the western and eastern sides of the Arctic regions is designated by Y and Z respectively (which is not included in Google earth).

So how to Identify our position in UTM Zones ?

Red Point : 10L

Green Point : 12Q

Yellow Point : 6P

White Point : 11G

Lets take a closer look to how India Looks under Grid Lines ...

 So under which Zone does the State Gujarat fall ?

Some Parts in Zone 42 and a little part in Zone 43 ? Lets take a more closer look ...

How to find Northing ?

Northing coordinate is the distance of any point from the equator.

To find Northing, we consider the equator as our reference line. 

If we are moving upwards from equator, i.e., in Northern hemisphere then our reference line (equator) will be at 0 m (zero metre) and the value will increase as we move towards the North Pole.

If we are moving downwards to the equator, i.e., in Southern Hemisphere then our reference line (equator) will be at 10,000,000 m (10⁷ metres) and the value will decrease to zero as we approach the South Pole.

Note: Here we have used 10⁷m to avoid negative values as move below to equator. Which means if we are at 6,000,000 m below the equator, then inspite of writing -6,000,000 m , we are going to write 4,000,000 m ( = 10,000,000 - 6,000,000) .

How to Find the Easting ? 

To determine the Easing, One should have a knowledge of Central Meridian.

Let us Consider any particular Zone on the UTM Grid as shown by red line in figure below :

Since the upper portion is a curved edge, so it we peel out this piece and paste on a plat surface, we get a shape as shown below :

It is to be noted that the zones are further subdivided into an eastern and western half by drawing a line down the middle of the zone. This line is known as the central meridian and is the only line within the zone that can be drawn between the poles and be perpendicular to the equator 

Every Zone has a separate Central meridian.

Now we will consider central meridian as our reference line for finding the Easting coordinate.

The central meridian has been assigned a value of 500,000 m.

If our point is located to the east of central meridian the value will exceed from 500,000 m to that point. So if we are at 100,000 m to east of central meridian, our easting coordinate will be 600,000 m E (= 500,000 + 100,000)

If our point is located to the west of central meridian, the value will decrease from 500,000 m to that point. So if we are at 100,000 m to west of central meridian, our easting coordinate will be 400,000 m E (= 500,000 - 100,000) 

Note :  An easting of zero will never occur, since a 6° wide zone is never more than 674,000 meters wide.

See the figure below : At the edge of the Zone the easting coordinate is not zero (figure a, where the red arrow indicates the position of mouse pointer) and since our location is to the west of the central meridian of Zone 43, the value of Easting coordinate is luss than 500,000 m (figure b, where the red arrow indicates the position of mouse pointer) .

Minimum and maximum easting values are:

160,000 mE and 834,000 mE at the equator

465,000 mE and 515,000 mE at 84° N

Benifits of using UTM :

✓ No negative numbers or East-West designators.

✓ Coordinates are decimal based so no more minutes and seconds to convert.

✓ Coordinates are measured in metric units.

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