An accurate, reliable system of station identifiers comprises the very foundation of meteorology,
because the most popular data exchange formats (SYNOP, METAR, and many climatological records) use
station identifiers or call signs, not latitude/longitude coordinates. Unfortunately, finding the
latitude and longitude is not always simple, and there are a number of problems. For example, identifiers
are sometimes changed or "moved" to a new location. The call letters "KAUS" and "KDEN" are prominent
examples of identifiers which were moved to new locations, creating potential problems in the climate
record. Also in some countries, identifier assignments and changes in their use tend to be poorly
documented. This is a major problem for us meteorologists and climatologists who are processing and
exchanging weather information in our increasingly globalized world.
Master Location Identifier Database (MLID)Weather Graphics publishes the Master Location Identifier Database (MLID). This is a list of about 45,000 worldwide station identifiers which harmonizes thousands of ICAO, FAA, WMO, WBAN, and special use codes, standardizing place names according to ISO 3166 guidelines. It now includes integration of the latest FAA, ICAO, and WMO identifiers, making it the most up-to-date database available anywhere. This list only includes government-operated stations which are commonly available on NOAAPORT, GTS, and AFTN circuits. The MLID includes numerous historical stations, which tend to be omitted from government databases without any documention. Weather Graphics started developing the MLID in 2006 to meet the rigorous standards required by some of our contract climatological work. The MLID was developed because the existing comprehensive sources like MASLIB, NCDC's station list, and ISH are either outdated, contain errors, are lacking useful metadata, or are not adequately harmonized.
SourcesAll identifiers are obtained from primary sources: directly from the ICAO, the FAA, Transport Canada, the NWS, and the WMO. Where these sources are lacking, erroneous, or missing, the database undergoes further corrections. Historical assignments are obtained from these sources along with AFWA and NCDC, though the station database of NCDC contains a few errors which we have corrected. There are numerous sites on the Internet that crowdsource identifier information which is unverified and in some cases erroneous. Therefore we rely strictly on primary sources of data. Unsourced information from the Internet is not used. It should be noted that we also carefully distinguish NWS identifiers, which are often the cause of misplaced data. For example many listings use the NEXRAD radar site location of KGRK when the airport 34 miles away uses KGRK for surface observations.
History of the MLIDAs a meteorologist I first started developing identifier lists for my earliest weather analysis programs: RadarScan, which eventually became WeatherGraphix and Digital Atmosphere. These required increasing levels of accuracy and integrity. From 1996 to 1998 I was a weather systems programmer at Det 7 AFGWC at Tinker AFB, the Air Force agency which maintains weather station identifier assignments. This gave me firsthand experience with the maintenance process. Some of my climatology work in recent years has required accurate crossreferencing of identifiers, so this database not only seeks the most up-to-date assignments but also tracks changes and crossreferences accurately between ICAO, FAA, WMO, and WBAN.
Standard version vs. Professional VersionDue to the time invested in maintaining MLID we require fees for its upkeep. As a result we have divided the project into a free Standard Version and a paid Professional Version. The Professional Version adds station history of identifier changes over the years going back to the 1940s and the known dates. It also adds quality flags, postal code, crossreference data (to map old identifiers to new ones), add/deletion dates, and plaintext development notes. Significant amounts of information on historical National Weather Service radar locations and forecast offices exists for the United States Additionally, the Professional Version is the sole version permitted for use in commercial projects. A Professional Version sample (containing only Argentina, Western Australia, Manitoba, Scotland, Primorsky Krai in Russia, and Texas) in Excel format may be downloaded here (500 KB).
The Standard version may be downloaded here:
CSV version: master-location-identifier-database-202401_standard.csv
Excel version: master-location-identifier-database-202401_standard.xls
LicensingThe MLID project represents literally thousands of hours of work, and a significant amount of the updates are still done by hand to ensure accuracy. User fees are essential for supporting the efforts required to source information and keep this database current. However we also understand the value to the meteorology community, so we offer a Standard Version and a Professional Version.
■ Standard (free) version. This may be used in personal, educational, academic, research, and government projects. It may be downloaded from the link at the top of this document. The Standard Version may not be used in any commercial product or service. Use is subject to the Creative Commons Attribution / Non-Commercial (BY-NC) license.
■ Professional Version. This allows you to use the MLID in any project, including for commercial use. This version is a highly expanded version of the MLID.
Lifetime updatesIf you have purchased the Professional Version, you may subscribe and get updates. To begin a subscription, click here. ($149/yr). Each purchase (quantity) is for ONE year. During the subscription period you are entitled to all updates that we produce, including the first update that follows the end of your subscription period. As a licensed user, you may renew expired or lapsed subscriptions at any time in the future without any extra charge.
DisclaimerWhile our goal is to provide the most complete and accurate station listing possible, the MLID is provided without warranty and we caution users that errors may exist in the database without our knowledge. There is no refund of MLID purchases, so we encourage you to inspect all of the provided sample data to make sure it is suitable for your needs.
ImprovementsSuggestions, comments, and corrections are welcome. You may send these to our contact page.
Current versionThe current version is:
Edition 2022.07 | July 2022 | Series E
Effective dates: FAA: 2022-06-16 | ICAO: 2022-06-16 (AIRAC 2206) | WMO: 2022-07-01
DocumentationThe MLID is fully documented in this PDF file: master-location-identifier-database-202103.pdf (394 KB, Updated March 2021)
An overview of identifier schemesCoded station identifier schemes were developed by radio and telegraph operators at the turn of the 20th century. However, meteorology suffered greatly from a lack of coded observation standards and reports were normally filed under the call letters of the teletype station. The United States and Canada began using airport identifier codes domestically around 1948 for their "surface airways observation" (SAO) program. At the same time, the International Meteorological Organization finally devised a standard numerical code form for synoptic reports along with a worldwide station identifier scheme. Then in the mid-1950s, the International Civil Aviation Organization created a global airport identifier scheme, which was slow to catch on but allowed for the proliferation of airport-based METAR weather observations by the 1960s. This soon eclipsed the SAO system in the United States and Canada and forced its retirement.
Fifty years later, these three schemes still form the bulk of most traditional weather observations today. Listed here are these and a few other identifier schemes used in meteorology and aviation weather:
World Meteorological Organization (WMO) identifiersThe WMO identifier scheme was introduced in 1947 by the International Meteorological Organization (later the WMO) Conference of Directors to support the "International Meteorological Code", which was put forward to replace numerous incompatible formats used by national weather agencies across the world. The WMO identifier, often called the "index number" relies on a 5-digit numeric code to identify a land weather station. The first two digits are referred to as the "block number" and refer to the geographic area (00-29 Europe, 30-59 Asia, 60-68 Africa, 69 special use, 70-79 North America, 80-89 South America, 90-99 Oceania). The last three digits are loosely referred to as the "station number". Fortunately the WMO provides free access to all WMO identifier assignments on its website. The code remains widely used in synoptic ("6-hourly") weather reports and particularly in upper air (radiosonde and rawinsonde) reports to this day. As of September 2018 there were 18,762 WMO identifier assignments in current use.
International Civil Aviation Organization (ICAO) Location IndicatorsThe ICAO location indicator system was developed in 1946 by the International Civil Aviation Administration. These indicators were not widely used until the 1950s. They were updated as biannual amendments until 1967 when the system was published formally. The ICAO code consists of 4-letter identifiers managed at the state (national) level in section GEN 2.4 of the ICAO-standardized Aeronautical Information Publication and then diffused by the ICAO to other countries. Some ICAO identifiers are considered national-level indicators, used within the country but not published internationally. Some examples of nonpublished ICAO indicators are the codes for minor airports in the United States (e.g. KCDS, Childress TX). Russia also has a number of stations beginning with the letter X (the Russian letter "yer" as it appears on ITU-2 compliant teletype) for a handful of military airfields and domestic airports. As of September 2018, there were 22,503 ICAO indicator assignments in current use.
SPECIAL NOTE: In our MLID list above, we categorically prohibit WSR-88D radars from possessing an ICAO or FAA code, because this causes conflicts. For example, KGRK commonly refers to both an aerodrome and a radar site, when in fact they are separated by 35 miles.
Weather Bureau Army Navy (WBAN) identifierIn the 1950s and 1960s, computer programmers with the NWS found that it was difficult to work with weather data because some observations were transmitted with FAA LIDs, some were transmitted with WMO station indexes, and other data on paper or in old formats such as Copenhagen code had no number at all. So the WBAN scheme was developed, which was one of the first large-scale efforts to standardize meteorological identifiers. A WBAN identifier is a 5-digit identifier, similar in appearance to the WMO identifier but not equivalent. It is still used by NCDC to identify many of its climatological datasets and continues to be very important for meteorological work. However the WBAN is greatly limited since it was not used to its full potential; there are omissions in WBAN assignments throughout the U.S. reporting network, and no WBAN assignments exist outside the U.S. except those which operated under the authority of the Department of Defense or other Federal agenices. NCDC provides free access to all known WBAN identifier assignments.
Master Station Library (MASLIB) Catalog NumberThe MASLIB scheme was developed in the 1960s by Air Force Global Weather Center (AFGWC), now part of Air Force Weather Agency (AFWA). It was created to overcome shortfalls in the WBAN system, which is geared mostly for climatology, and assist AFGWC/AFWA with routing and processing data in real-time. AFGWC/AFWA has maintained the MASLIB for over 40 years, though public releases ceased in 2000, presumably because of increased concerns with operations security. In January 2020, the operational organization managing the MASLIB, the 557th Weather Wing at Offutt AFB, Nebraska, denied our FOIA request to obtain a current or historical copy, citing exemption 3(b), 10 USC 130e, which exempts critical infrastructure security information. The MASLIB code consists of 6 numerical digits, and is heavily based on the WMO identifier. In fact, if an identifier has a WMO assignment, its MASLIB number will be the WMO identifier suffixed with zero. Even if a station does not have a WMO identifier, it will have a MASLIB number very similar to that of neighboring stations that do have a WMO identifier.
Environment Canada location identifierCanada uses a system of 3-letters identifiers based heavily on the FAA Location Identifier scheme. This system reserves Y-- identifiers for Canadian use. These are further prefixed with "C" to form Canada's ICAO assignments, though many special-use identifiers (below) have not been put forth specifically as ICAO assignments. The Canadian system grew out of a 2-letter teletype scheme developed in the 1940s which was prefixed with "Y" by the United States to maintain compatibility with its circuits (e.g. Toronto was "YZ" and became "YYZ"). Starting in the 1980s, Canada began using a system of special-use identifiers starting with W for climate stations and Z for aviation. These have become part of the standard Canadian identifier system. However by the 2000s many other special-use identifiers were adopted, such as A for agromet, V for sports venues, and X for special use. Due to the possibility of numerous conflicts with 3-letter FAA identifiers, only Canadian identifiers W, X, Y, and Z are treated as standard and are directly transcoded to the FAA system. All other identifiers are not treated as an ICAO unless they have been reported to the ICAO as an identifier assignment or have been used to transmit data in the past (many agromet stations, for example, do not transmit data under their identifier). Canadian identifiers are assigned by Transport Canada and Environment Canada.
International Air Transport Association IdentifierThe IATA identifier is a 3-letter code that identifies a specific worldwide airport. It is generally used by the airline industry for ticketing, baggage. IATA identifiers are not generally used in meteorology. As of September 2010, there were officially 6,071 IATA airport assignments. It should be noted that the IATA charges $346 to $1100 for direct access to its catalogue of IATA identifier assignments.
Problems with crossreferencingMeteorologists, and to a certain extent, pilots, all have to be aware of pitfalls and other issues arising from the multiple identifier schemes that are in use today.
Casual reassignmentIdentifiers are not permanently fixed to a location and are sometimes "moved" by identifier authorities. This is often done for the convenience of the public. This is an especially serious problem because any person using products from many years ago or trying to analyze climatological information may end up with erroneous results. In the U.S., minor identifiers are commonly retired for 20 or 30 years and then assigned to a new location. This in itself causes little trouble. However, overnight uprooting of major airports does occur from time to time. Prominent examples are the movement of "DEN" from Stapleton to DIA and the movement of "AUS" from Mueller Airport to Bergstrom Field. Analysts have to know start and end dates for identifiers, and these are not always available from sources.
Inadequate documentationThere are deficiencies in the station lists caused by poorly documented station locations. The latter is especially a problem with ICAO identifiers.
KQ identifiersThe KQ-- ICAO identifier block is reserved by the U.S. Department of Defense for special use. Some of the identifiers have been assigned for routine use and their information is known (such as KQCU for Fort Chaffee and KQWS for Fort Drum; many are listed in this source). Other identifiers are used for classified or for-official-use-only operating locations, quite often for deployed combat weather teams. The MLID provides assignments which have become public knowledge and can be reasonably verified, but due to the withdrawal of the MASLIB from public access there is no way to confirm the information or determine start and stop dates. These should be considered to be for informational purposes only. A different special use identifier of significant public interest, KXTA, is believed to be assigned to Area 51 (Groom Lake), Nevada, but since this has never been verified in primary source documents it is our policy to not include it in the MLID.
Non-colocated stationsWeather stations are not necessarily at airports and may be in weather "observatories". This is common in countries like the former USSR. Unfortunately the WMO listings often fail to identify where in a community a weather station is, and this is compounded by imprecise location coordinates. As a result, some aggregated identifier listings may erroneously place a site at the nearest airfield or in a city center location.
RomanizationRomanization is a common problem plaguing station listings, especially when older or inconsistent systems are used. The WMO still uses the older GOST system for Russian, for example, and some entries originating from MASLIB and US government sources use Wade-Giles and even Postal Map Romanization for China rather than Pinyin. Our MLID database works toward standardizing and modernizing these entries: for example we use BGN/PCGN for Russia, Pinyin for China, and both Wade-Giles and Pinyin for Taiwan.
Sources of station identifier informationNOTE: A lot of this section was written in 2010. In January 2023 I updated the links and removed a few unimportant sites that no longer exist.
Over the years I have subdivided various sources into three categories: cardinal, secondary, and tertiary. Cardinal sources are authoritative documents from key agencies which have jurisdiction over identifier assignments at the international or national level. This is the sole source of MLID information. Secondary sources are key government listings used in operational systems but which do not carry authority over assignments. Tertiary sources are sources in the hobby and private industry sector that collect and distribute identifier information and may contain errors.