Grid squares
From Megawiki
Maidenhead locators are also commonly referred to as grid locators or grid squares, despite having a non-square shape on almost any cartographic projection.
A grid square or Maidenhead locator represents a position on the Earth based on latitude and longitude. This position information is presented in a limited level of precision in order to limit the amount of characters needed for its transmission using speech or Morse code.
Chosen coding uses alternating pairs of letters and digits, and in each pair the first character encodes longitude and the second character encodes latitude, like so:
EN62bq55
These character pairs have also traditional names, and in case of letters the amount of characters (or "encoding base number") used in each pair does vary.
In order to avoid negative numbers in the input data, the system also specifies that latitude is measured from southpole to northpole giving south the value of zero, and north value of 180°.
To simplify manual encoding, first base number was chosen to be 18, thus dividing the globe to 18 zones of latitude of 10° each, and 18 zones of longitude 20° each. These zones are encoded with letters "A" to "R", and this pair of letters is traditionally called field.
Further subdivision is done with base number of 10 and encoding as digits "0" to "9", and this resulting digit pair is called square. This is where the alternative name "grid squares" comes from. Each of these squares represents 1° of latitude by 2° of longitude.
The square is denoted by the two digits following the field letters in the Maidenhead locator. To give an example, Newington, Connecticut, home of W1AW, the American Radio Relay League's Maxim Memorial Station, is found in grid locator FN31.
For additional precision, each square can be sub-divided further, into subsquares. These are encoded by letters often (but not always) presented in lowercase, and again to ease earlier manual encoding calculations from degrees and minutes, the base number was chosen to be 24 giving these subsquares dimensions of 2.5' of latitude by 5' of longitude.
Today, Maidenhead locators are used and recognized by radio amateur individuals and organizations around the world. Many utilities exist to convert latitude and longitude to locators, as this is a favorite hack for programmers who are also radio amateurs. Commercially available (civil) Global Positioning System receivers are frequently able to display Maidenhead locators.
Maidenhead locators are used as part of the formulas for scoring in many VHF amateur radio contests. Grid locators are also the basis of earning the American Radio Relay League's VHF/UHF Century Club operating award.
