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 pitfalls. 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. Also, with some agencies and identifier systems, changes tend to be poorly documented and poorly published. This is a major problem for us meteorologists and climatologists who are processing and exchanging weather information in our increasingly globalized world. I have created this resource specifically to help the community understand and maintain accurate station listings.

1. Master Location Identifier Database (MLID)

Weather Graphics publishes the Master Location Identifier Database (MLID). This is a list of about 41,000 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 are regrettably omitted from most current government databases (closed airports, CAA airfields, etc). Weather Graphics started developing the MLID in 2006 to meet the rigorous standards required by some of our contract climatological work. We found that most comprehensive sources like MASLIB, NCDC's station list, and ISH are greatly outdated, contain errors, or are not adequately harmonized.

1. Downloads. The MLID may be downloaded here. For best results, right-click on the link and use "Save As..."

2. Sources. All 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 excellent databases of identifiers on the Internet, such as Airnav and OurAirports.com, and these should certainly be visited for browsing individual stations. However these sites republish available data, same as we do, and are not well cross-referenced. Furthermore OurAirports crowdsources identifiers and in 2011 we discovered numerous errors, in which ICAO identifiers were listed which could not be found in any governing documents. Therefore we do not use secondary sources of data. It should be noted that we also carefully distinguish NWS identifiers: for example many databases contain erroneous coordinates for KGRK, with errors of up to 34 miles because distinctions are not made between the ICAO identifier and the NWS identifier.

3. Origin. 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. During the 1990s I also worked for Det 7 AFGWC, the Air Force agency which maintains weather station identifier assignments, and this gave me a lot of firsthand experience with sourcing and maintaining this data. 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.

4. Licensing. The MLID project represents countless hours of development work. User fees are essential for supporting the efforts required to source information and keep this database current. You may receive the latest version and subscribe to updates here:
  ■ Purchase the MLID: To purchase the MLID, click here ($295). This licenses you to use the MLID and subscribe to updates now or at any time in the future.
  ■ Subscriptions: In addition to the base price, you may subscribe and get updates every month. This service is priced at $190/month or $575/year . For multiple months or years, set the "units" to the number of months or years you want to subscribe. We recommend purchasing no more than 3 years at a time. As a licensed user, you may renew expired or lapsed subscriptions at any time in the future without any extra charge.
  ■ Disclaimer: While 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 the 2013 sample data above to make sure it is suitable for your needs.
  ■ Personal/educational prices: Unfortunately we cannot provide free or educational versions of this database, because funds are essential for its ongoing development. You are welcome to use the 2013 version above in your personal and commercial projects.
  ■ View your cart: View your cart or complete your purchase here.

5. Improvements. Suggestions, comments, and corrections are welcome. You may send these to our contact page.

2. An overview of identifier schemes

Coded 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) identifiers
      The WMO identifier scheme was introduced in 1948 by the International Meteorological Organization (later the WMO) 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 August 2013 there were 12,912 WMO assignments offically assigned.

International Civil Aviation Organization (ICAO) Location Indicators
      The ICAO location indicator system was developed around 1955 by the International Civil Aviation Administration, updated as biannual amendments until 1967 when the system was published formally. The ICAO code consists of 4-letter identifiers published 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 December 2012, there were 10,774 ICAO assignments officially assigned.
      A 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.

Federal Aviation Administration (FAA) Location Identifiers
      The FAA location identifier (FAA LID) is a 3- or 4-digit alphanumeric designator. The Civil Aeronautics Administration began publishing three-letter identifiers starting in the 1940s. These were mostly for internal use and did not start appearing in planning documents for pilots until the mid-1960s. Use of the FAA LID ceased for observational coding purposes in 1996, but it is still widely used for aeronautical purposes in the U.S. and in some meteorological discussion products. In many cases, a three-digit identifier can be "converted" to its ICAO form by adding the appropriate ICAO region letter as the first letter. However this is NOT a reliable rule, especially in Alaska and Hawaii. While ANC may translate correctly to PANC, there are many stations where this is not the case, such as BRW, which is PABR under the ICAO form. This is a significant source of errors in some crossreference tables. As of June 2013, there were 5431 FAA identifiers officially assigned (not counting 4-character ones, which are not used for meteorological work).

Weather Bureau Army Navy (WBAN) identifier
      In 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 Number
      The 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 after 1999, presumably because of increased concerns with operations security. 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 identifier
      Canada bases their identifiers heavily on the FAA Location Identifier scheme, adopting most identifiers out of the Y-- block out of a memorandum of agreement with the FAA. Starting in the 1980s, Canada also began using identifiers starting with W (for climate stations), Z (for special use aviation), and X (for miscellaneous stations). Canadian identifiers are assigned by Transport Canada and Environment Canada. The Canadian METSTAT history tables indicate that Canada has begun using identifiers starting with other parts of the alphabet, such as A for agromet and V for sports venues. It appears this may begin causing numerous identifier conflicts in the near future, so there is the possibility we may have to begin separating the two in our MLID database and harmonizing those schemes.

International Air Transport Association Identifier
      The 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.

3. Problems with crossreferencing.

Meteorologists, 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.

1. Uprooting. Identifiers are not permanently fixed to a location and are sometimes "moved" by government officials, a process known as uprooting. 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.

2. Inadequate documentation. There are deficiencies in the station lists caused by poorly documented station locations. The latter is especially a problem with ICAO identifiers.

3. KQ identifiers. The 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 (1) classified operating locations and (2) for deployed combat weather teams. Their association with a geographic location is usually classified or marked for official use only.

4. Weather 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. Also, some of the "guessed" locations in older MASLIB sources are based on town locations and may not represent the actual location.

5. Romanization 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 these entries: for example using BGN/PCGN for Russia, Pinyin for China, and both Wade-Giles and Pinyin for Taiwan.

4. Sources of station identifier information.

Over the years I have subdivided various sources into three categories: cardinal, secondary, and tertiary. The cardinal sources are authoritative documents from key agencies which have jurisdiction over identifier assignments at the international or national level. Secondary sources are important government listings which are not empowered with authority over assignments. Tertiary sources are mostly sources in the hobby and private industry sector that collect and distribute identifier information.

Resource ICAO FAA WMO WBAN Special Coordinates CARDINAL SOURCES WMO Pub 9 A This is the sole, authoritative source of synoptic identifier numbers. Thankfully the WMO does a great job of putting its publications online, and this up-to-date resource can be consulted for all the synoptic identifiers that might be encountered. One significant problem is some coordinates are slightly misplaced, largely due to a lack of quality control among some of the member nations which supply the data.         Location Indicators, ICAO Publication 7910 (ordering info only) is the sole authoritative source for worldwide ICAO identifiers. The database is available in printed form without coordinates, and in electronic form with coordinates. The ICAO has made great improvements in recent years in the accuracy and integrity of location data.           NOTAMS ICAO lookup provides ICAO information. Since it is approved for navigational use, presumably this listing reflects the latest data in ICAO Pub. 7910. It does appear to contain the newest airports around the world. Note that "LOC ID" in this database is equivalent to the FAA location ID. But as is common with authoritative ICAO data, there's no coordinates.           Location Identifiers, FAA Publication FAAO 7350 is the sole, authoritative source for ICAO identifiers in the United States, where it overrides ICAO Pub 7910. It includes non-authoritative information about Canadian ICAO identifiers. Although 7350.7 is fully online, position information is not available in either the online or printed version.   USA         National Flight Information Database is an operational database that incorporates all FAA data on its identifiers. USA USA       USA Canadian METSTAT Tables are the sole authoritative source of all Canadian identifiers. Abbrevations include A=Airport; RCS=Reference Climate Station; CDA=Canada Department of Agriculture; AGDM=Agricultural Drought Monitoring Station; LWIS=Limited Weather Information System. CAN   CAN     CAN Australian Bureau of Meteorology Station List Files is the sole authoritative source of Australia's station identifier information online. Data files are organized in both alphabetical and station number order, for the whole of Australia, and by individual states. (Thanks to Peter Creswick) AUS   AUS   AUS   SECONDARY SOURCES US Air Force Master Station Catalog (MASLIB). The MASLIB catalog has for decades been the single most important source of crossreferenced identifiers. It does contain some errors here and there, and unfortunately is no longer available presumably due to post-9/11 operations security issues. Archived versions are posted here, obtained from UCAR datasets: 1967, 1973, 1976, 1994, 1995, 1996, 1997, 1998, 1999.   NCDC Station Locator is a good source of U.S. station information, but it seems to be running about 2 years behind on updates as it misses a lot of the ASOS stations; I have also noticed a few errors here and there. The raw station inventories can be found here (raw directory listing), along with a massive station history flatfile called MASTER-STN-HIST.TXT (32 MB). (Due to size, archive copy is not kept on this server; we will put one online if NCDC ever goes down). USA USA USA USA USA USA NCDC Multinetwork Metadata List is another decent government source that includes WBAN numbers. It seems to lack a lot of the newer ASOS stations and may have originated from the same database as NCDC Station Locator. USA USA USA USA USA USA NOAA's Platform Name list is helpful for making sense of offshore identifiers.           NWS/TG Table contains thorough listings but from unknown sources and for an unknown purpose. (Also see table with K--- identifiers sorted by identifier).       NWS Meteorological Station Information Lookup is the National Weather Service's "public" station database. While the interface is promising, its data is outdated and it does not contain many of the newer ASOS sites. This is probably simply a web interface for the flatfile above (NSD.TXT).     Greg Thompson (NCAR/RAP) Station Table is very good and updated often! It is a must-see. An older version is mirrored at the FAA ADDS Weather site. Note that there is no provision for older stations and it appears that the distinction is blurred between FAA and IATA identifiers.     NWS Data Review Group processes and archives Requests for Change to its various datastreams (NWSTG, NOAAPORT, FOS, NWWS, AWIPS, AFOS). Identifier changes can sometimes be found in these documents. (AS OF 2009 THIS APPEARS TO HAVE BEEN PASSWORD PROTECTED)           NWS Systems Operations Center Change Notices are another source for finding new identifiers by combing through datastream changes to the NWSTG system.           METEO France is another exhaustive database of stations (no position info). A backup copy (dated 8 Jan 1999, retrieved 25 May 2009) is archived here. OLD   OLD       ECCAIRS Location Indicators list by the European Coordination Centre for Accident and Incident Reporting Systems appears to be an authoritative derivation of ICAO Pub 7910 and thus provides a valuable supplementary source of ICAO identifiers. Unfortunately it has not been updated since January 2006 and is now considered stale. An archival copy is made available here. OLD         OLD EUROCONTROL used to maintain a current ICAO reference list at this link. However their page states "in December 2007, we have now closed the public access to the tool for searching ICAO 7910 location indicators and their location names. We hope that you have had the time to prepare for an alternative procedure for consulting these codes." CANX           Digital Aeronautical Flight Information File (DAFIF) is produced by the United States government as a comprehensive navigational database approved for flight operations. This provides information on many ICAO and FAA identifiers. Unfortunately its producers, the National Geospatial-Intelligence Agency, withdrew the product from public access citing intellectual property issues. Data from DAFIF still makes up the vast majority of international identifier information on aviation websites. CANX CANX     CANX NAV CANADA's TAF Interface is about the only "official" source of Canada's METAR identifier information online. This is a crude way of obtaining a few of some of the more obscure ones. CANADA           Environment Canada's Synoptic Station List shows synoptic identifiers within Canada, in WMO Pub 9 A format (thanks to Christine Hudnall for finding the new version). A backup copy (dated May 2009, retrieved 25 May 2009) is archived here.           TERTIARY SOURCES British Atmospheric Data Centre Historical International Station Catalogue Historical International Station Catalogue - This index is somewhat outdated and similar to the MASLIB, but due to the historical slant I have found this useful for researching identifier changes, especially outside the U.S. It can be used in conjunction with a similar NCDC product. A backup copy (dated 3 Nov 1998, retrieved 25 May 2009) is archived here (1.8 MB).           British Atmospheric Data Centre Historical International Station Catalogue Historical International Station Catalogue - This index is somewhat outdated and similar to the MASLIB, but due to the historical slant I have found this useful for researching identifier changes, especially outside the U.S. It can be used in conjunction with a similar NCDC product. A backup copy (dated 3 Nov 1998, retrieved 25 May 2009) is archived here (1.8 MB).           Philip Gladstone's CWOP - This I have found useful for researching is pretty thorough and has many different weather databases crossreferenced. You can also check this list. The problems with this list is it omits various WMO and WBAN identifiers and does not have historical identifier information.           AIRNAV is a high-traffic aviation website that is useful for finding exact information about any airfield. It has been of use for finding new airfields with obscure ICAO / FAA identifiers.           World Aero Data is another good aviation identifier site. It appears it draws mostly on the withdrawn DAFIF product.       OurAirports.com is another source of ICAO information. However in 2010 we found a lot of questionable ICAO entries and it appears that there is not much quality control of user submissions.       OpenFlights is a collaborative attempt to pick up where DAFIF left off. One problem with this project is the blurring of IATA and FAA identifiers, which in meteorological use can cause numerous conflicts with historical data.

5. Other investigation resources.

1. LatLonToElevation allows fast calculation of unknown elevations using the National Elevation Dataset and Shuttle Radar Topography Mission.

2. METAR Maintenance, a short page by Joe Wakefield, describes what is involved in updating AWIPS with new stations.

3. Country codes. This interface to geonames.org determines which country a given lat/long is in.

4. Place. This interface to geonames.org determines which place represents a given lat/long.

5. Time zones. To find the time zone used by a particular station, we recommend using the geonames.org database. Here is a convenient form for requesting data.

6. Elevation. This interface to geonames.org queries the SRTM (Shuttle Radar Topographic Mission) and returns an elevation in meters. However we've found that the Google Earth elevation readout gives considerably more accurate results, at least in the U.S. and Canada.