- Main article: Names
If the name can be spelled without an abbreviation, then don't abbreviate it. Computers can easily shorten words, but not the other way (St. could be Street or Saint). If the signs have abbreviated words and you don't know what the full word is, then use it temporarily until someone else completes it. Using short forms is a decision of software; i.e., the underlying data should have the full street name. This will allow a renderer, a router or a location finder to introduce abbreviations as necessary. See, for instance, the list of abbreviations used by Name Finder and Nominatim.
If the name is incorrect when spelled in full, however, do not falsely expand it. (For example: Wilts & Berks Canal, British placenames beginning with "St", Invalid abbreviation expansion) If modifying a name creates ambiguity (for instance, by local convention St. John's is in Newfoundland, while Saint John is in New Brunswick) it's best to keep the local usage intact.
The name "Cedar St" on a sign, which is abbreviated to save space, should be completed to Cedar Street, but the name John F. Kennedy Boulevard is not expanded to John Fitzgerald Kennedy Boulevard in English speaking countries, since the shorter version is the common spelling and pronunciation. With some (academic) titles in names the abbreviated version is also the most commonly spelled version.
Apart from following the above rules, you should always enter the full name as it appears on the street name signs but be aware that street signs may contain errors.
This guidance about abbreviations applies not only to street names but also street addresses in addr:street=*, which should generally match the names of the corresponding streets. (This example Sophox query shows how to find street addresses that incorrectly contain abbreviations in a specific language and geography.)
Contrary to the guidance above, in Canada, it is sometimes but not always the practice to abbreviate city quadrant suffixes and omit ordinal indicators. For example, "6th Street Northwest" might be tagged as "6 Street NW". There is no set policy as to which locations in Canada use the fully-expanded name and which locations use the abbreviated format. The practice is more prevalent in certain parts of the province of Alberta, however, locals familiar with the situation note that the exact reason for this tagging practice is unclear. The quadrant suffixes are spoken verbally in their expanded form, however some have posited that this spoken form of the NW-SW-NE-SE quadrant suffixes are not abbreviations but rather an idiosyncratic local pronounciation.
Mappers should consult the talk-ca mailing list in order to determine which convention applies in a specific province, region, city, or neighborhood in Canada. Data consumers, especially navigation applications, should also consult the local community in order to determine the specific rules about whether a given area's street names need to be expanded before sending them to a text-to-speech (TTS) engine.
When most of the roads in the U.S. were imported from TIGER in 2008, each road's name=* tag contained abbreviations. In 2012, a bot automatically expanded most abbreviations following a community discussion. However, some abbreviated street names remain, either because the bot failed to detect them or because of subsequent edits by inexperienced mappers.
In American English, "St." is usually considered to be an abbreviation of either "Saint" or "Street". Therefore, the city of St. Louis, Missouri, is tagged name=Saint Louis, even though the proper written style is "St. Louis". However, when "St." is part of a family name, the expanded form "Saint" is usually considered a misspelling, thus "Lake Saint Clair" (named after the saint) but "St. Clair Township" (named after Arthur St. Clair).
Tagging idiosyncratic abbreviations explicitly
When a feature has an abbreviation that is idiosyncratic rather than systematic, tagging the abbreviation explicitly allows data consumers to discover the abbreviation without overloading the usual abbreviation tables with extremely rare abbreviations. In English, it isn't always the case that you can abbreviate a compound word using an initialism, but sometimes a particular initialism or acronym is expected as an alternative to writing out the name in full. For example, "Centers for Disease Control and Prevention" should be abbreviated as "CDC" rather than "CDCP".
short_name=* is generally used to explicitly record abbreviations and other shortenings, but there are several common synonyms. ref=* is also used on some kinds of features, especially administrative boundaries, when the feature isn't also referred to by a numeric identifier.