Maidenhead Locator System

From Wikipedia, the free encyclopedia

The Maidenhead Locator System is a scheme used by amateur radio operators for identifying positions on the Earth. It was proposed by the British radio amateur Dr. John Morris (G4ANB), and later adopted by a group of VHF managers, meeting in Maidenhead, England in 1980. The Maidenhead Locator System supplants the older QRA locator system with one that is usable outside of Europe.

Maidenhead locators are also commonly referred to as grid locators or grid squares, despite having a non-square shape on almost any cartographic projection.

[edit] Description of the system

A 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, Morse code, or any other operating mode.

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:

BL11bh16

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°. (Geodetics counts things with "North positive".) For the longitude the definition is such that 180° west is zero and 180° east is 360°. (Geodetics counts things with "East positive")

To simplify manual encoding, first base number was chosen to be 18, thus dividing the globe into 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 a 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.

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.

The subsquare (when presented) is encoded into third pair of characters "A" to "X" which in US and UK are traditionally written in lower case letters. The corresponding Maidenhead subsquare locator is hence composed of two letters, two digits, two letters. To give an example, Newington, Connecticut, home of W1AW, the American Radio Relay League's Maxim Memorial Station, is found in grid locator FN31pq. Two points within the same Maidenhead subsquare are always less than 12 km apart. So a Maidenhead locator gives a lot of precision from a mere six characters, which are easily communicated.

Fields are divided into 100 squares each.
Fields are divided into 100 squares each.

For even more precise location mapping, additional two digits were proposed and ratified as extended locator making it altogether eight characters long, and dividing subsquares into even smaller ones. Such precision has uses in very short communication spans. Beyond this there is no specified common way to extend the system further into even smaller squares. Most often the extending is done by repeating alternating subsquare, and square rules (base numbers 24 and 10 respectively.) However, other bases for letter encodings have also been observed, and therefore such extended extended locators might not be compatible.

The Maidenhead locator system has been explicitly based on the WGS84 model of the earth's surface since 1999. Before that time, it was usually based on each user's local national land-survey coordinate systems, which do differ slightly from each other and the global WGS84. As a result, stations very near the edges of squares at denoted precision may have changed their locator in between previous convention, and use of WGS84.

To summarize:

  • Character pairs encode first longitude and then latitude
  • First pair (field) encodes with base 18 and letters "A" to "R"
  • Second pair (square) encodes with base 10 and digits "0" to "9"
  • Third pair (subsquare) encodes with base 24 and letters "A" to "X"
  • Fourth pair (extended square) encodes with base 10 and digits "0" to "9"
  • Fifth pair and onwards is not defined, but repeat of the third and fourth pair algorithms is one way:
BL11bh16oo66

At HF frequencies, positions are reported at square precision, at VHF and UHF usually at subsquare precision. More precise position reports are very rarely used.

[edit] Use by radio amateurs

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.

In IARU Region 1 rules, VHF distances are calculated from maidenhead subsquare centers using spherical earth. This results in a small error in distance, but makes calculation very much simpler, and given the inherent imprecision in the used input data, is not the biggest error source.

[edit] External links