The locator is a 6 characters word, expressing the geographical coordinates
of a location, a longitude and a latitude.
In the past, it was in use a 5 characters locator, but it was not
unique: the same locator identified a location in the European continent
and at the same time another place in Northern America and so on.
The new locator is thus called also worldwide locator (WWL).
The first 2 characters of a locator are letters, from A to R, and they
are followed by 2 digits and then by another 2 letters, this time ranging
from A to X.
Odd positions (first, third and fifth) specify the longitude while
even positions (second, fourth and sixth) specify the latitude.
As an example, let's look at the locator JM88CX (a random choice).
| J | The first character specifies the starting longitude. Each letters is equivalent to 20 degrees, from A (180 degrees west) to R (160 degrees east). In this case J=0 degrees. |
|---|---|
| M | The second character specifies the starting latitude. Each letter is equivalent to 10 degrees, from A (90 degrees south) to R (80 degrees north). In this case M=30 degrees north. |
| 8 | The third character specifies a longitude increment towards east and each digit is 2 degrees. In this case 8=16 degrees. |
| 8 | The fourth character specifies a latitude increment towards north, and each digit is 1 degree. In this case 8=8 degrees. |
| C | The fifth character indicate a further longitude increment and each letter (from A to X) is equivalent to 5 minutes (1/12 of degree). In this case C=10 minutes. |
| X | The sixth character indicate a further latitude increment and each letter (from A to X) is equivalent to 2.5 minutes, that is 2 minutes and 30 seconds (1/24 of degree). In this case X=57 minutes and 30 seconds. |
Summing up values, we can find the coordinates of the lower left corner
of the rectangle identified by the locator.
Since it is more correct to tell the coordinates of the center of the
rectangle, we must add also the fixed values of 2 minutes and 30 seconds
of longitude and 1 minute and 15 seconds of latitude (size of
half rectangle).
So, the geographical coordinates corresponding to the locator JM88CX are:
How good is this coordinates method?
About latitudes, since the terrestrial meridian length is constant and equal to about 40,000 km,
the locators range spans half of a meridian and there are 4320 locators (in vertical), what we can
say is that a locator's height is about 4.63 km.
Since the maximum distance of a point from the center of a rectangle is half rectangle (vertically),
the latitude precision of the locators method is constant and equal to about 2.315 km.
About longitudes, things are more complex, because the parallels' length change with the latitude.
Maximum length is at the equator, which is 40007.8 km long. Since there are 4320 locators
(horizontally), each is 9.261 km wide and thus the minimum precision for longitudes is
4.631 km.
Moving away from the equator, parallels are shorter, reaching zero length at the pole, thus
the precision of locators increases. We can use the following formula to estimate the longitude
precision at a given latitude:
Precision = 4.631 * cosine(latitude)
By the way, latitude is taken always as a positive number. As an example at 41° North, the
longitude precision of locators is:
In the worst case (equator), the maximum distance of a place from the center of the locator zone
is (simplified formula):
Distance = √(horiz_dist2 + vert_dist2) = √(4.6312+2.3152)=5.177 km
We can thus say that the locators precision is always better than about 5 km.
Radio amateurs do not compute only the connected countries, but also the different geographical locations, especially when using VHF and upper bands or when using amateur satellites.
A field is a rectangle identified by the first 2 characters of a locator
and is thus 20 degrees wide and 10 degrees tall.
For example the field JN goes from 0 to 20 degrees East and from 40 to 50 degrees North.
A square is a rectangle identified by the first 4 characters of a locator and is thus
2 degrees wide and 1 degree tall.
For example the square JN61 goes from 12 to 14 degrees East and from 41 to 42 degrees North.
To compute locators you can use the formula page on this site or, for italian locations, the Italoc program, from the software page.