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59-610: Topographic mapping in Canada was originally undertaken by many different agencies, with the Canadian Army’s Intelligence Branch forming a survey division to create a more standardized mapping system in 1904. The indexing system used today was established in 1923, and the map catalogue officially became the National Topographic System in 1926. The subdivision scheme that the National Topographic System uses

118-437: A geocode system is a locality-preserving hashing function . There are some common aspects of many geocodes (or geocode systems ) that can be used as classification criteria: The set of all geocodes used as unique identifiers of the cells of a full-coverage of the geographic surface (or any well-defined area like a country or the oceans), is a geocode system (also named geocode scheme ). The syntax and semantic of

177-413: A code word from some dictionary, and concatenation of such code words give us an encoded string. Variable-length codes are especially useful when clear text characters have different probabilities; see also entropy encoding . A prefix code is a code with the "prefix property": there is no valid code word in the system that is a prefix (start) of any other valid code word in the set. Huffman coding

236-598: A country , is also a valid postal code. Not all postal codes are geographic, and for some postal code systems, there are codes that are not geocodes (e.g. in UK system ). Samples, not a complete list: Geocodes in use for telephony or radio broadcasting scope: Geocodes in use and with specific scope: Other geocodes: Some standards and name servers include: ISO 3166, FIPS, INSEE, Geonames, IATA and ICAO . A number of commercial solutions have also been proposed: Code In communications and information processing , code

295-451: A hierarchical geocode system with same prefix represents different parts of the same location. For instance DE.NW.CE and DE.NW.BN represents geographically interior parts of DE.NW , the common prefix. Changing the subdivision criteria we can obtain other hierarchical systems. For example, for hydrological criteria there is a geocode system, the US's hydrologic unit code (HUC), that

354-504: A sequence of symbols over T. The extension C ′ {\displaystyle C'} of C {\displaystyle C} , is a homomorphism of S ∗ {\displaystyle S^{*}} into T ∗ {\displaystyle T^{*}} , which naturally maps each sequence of source symbols to a sequence of target symbols. In this section, we consider codes that encode each source (clear text) character by

413-418: A standards organization or governmental authority. So, the most general case is a table of standard names and the corresponding standard codes (and its official geometries). Strictly speaking, the "name" related to a geocode is a toponym , and the table (e.g. toponym to standard code) is the resource for toponym resolution : is the relationship process , usually effectuated by a software agent, between

472-432: A corresponding sequence of amino acids that form a protein molecule; a type of codon called a stop codon signals the end of the sequence. In mathematics , a Gödel code was the basis for the proof of Gödel 's incompleteness theorem . Here, the idea was to map mathematical notation to a natural number (using a Gödel numbering ). There are codes using colors, like traffic lights , the color code employed to mark

531-462: A fine-grained schema, by longer path of keys. For example, the Geohash 6vd2 , which is a base32 code, can be expanded to base4 0312312002 , which is also a schema with per-digit keys. Geometrically, each Geohash cell is a rectangle that subdivides space recurrently into 32 new rectangles, so, base4 subdividing into 4, is the encoding-expansion limit. The uniformity of shape and area of cells in

590-423: A form that the recipient understands, such as English or/and Spanish. One reason for coding is to enable communication in places where ordinary plain language , spoken or written, is difficult or impossible. For example, semaphore , where the configuration of flags held by a signaler or the arms of a semaphore tower encodes parts of the message, typically individual letters, and numbers. Another person standing

649-584: A front for the American Black Chamber run by Herbert Yardley between the First and Second World Wars. The purpose of most of these codes was to save on cable costs. The use of data coding for data compression predates the computer era; an early example is the telegraph Morse code where more-frequently used characters have shorter representations. Techniques such as Huffman coding are now used by computer-based algorithms to compress large data files into

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708-475: A given location has not been assigned an address by authorities. They can also be used as an "alternative address" if it can be converted to a Geo URI . Even if the geocode is not the official designation for a location, it can be used as a "local standard" to allow homes to receive deliveries, access emergency services, register to vote, etc. Geocodes in use, as postal codes . A geocode recognized by Universal Postal Union and adopted as "official postal code" by

767-419: A great distance away can interpret the flags and reproduce the words sent. In information theory and computer science , a code is usually considered as an algorithm that uniquely represents symbols from some source alphabet , by encoded strings, which may be in some other target alphabet. An extension of the code for representing sequences of symbols over the source alphabet is obtained by concatenating

826-564: A grid can be important for other uses, like spatial statistics . There are standard ways to build a grid covering the entire globe with cells of equal area, regular shape and other properties: Discrete Global Grid System (DGGS) is a series of discrete global grids satisfying all standardized requirements defined in 2017 by the OGC . When human-readable codes obtained from cell identifiers of a DGGS are also standardized, it can be classified as DGGS based geocode system . There are also mixed systems, using

885-400: A kind of "system of standard names". In the geocode context, space partitioning is the process of dividing a geographical space into two or more disjoint subsets , resulting in a mosaic of subdivisions. Each subdivision can be partitioned again, recursively , resulting in an hierarchical mosaic. When subdivisions's names are expressed as codes, and code syntax can be decomposed into

944-445: A letter (e.g., M ); and each map area divided into 1:50,000 scale "map sheets", denoted by a number (e.g., 13 ). These numbers and letters are then combined to form a unique designator for a map sheet, in this case, 30M13 Bolton , identifying a map sheet which includes the city of Vaughan, Ontario . Some map sheets are further sub-divided at their central meridian into two 1:50,000 scale "half-sheets", with an E or W appended onto

1003-511: A map series number to three digits using leading zeroes, the last digit in a map series number indicates a specific range of latitudes, and the number formed by the other digits indicates a specific range of longitudes. In the High Arctic zone, map series numbers are three digits, with the first two digits of each number inherited from the two map series in the Arctic zone immediately to the south. In

1062-409: A mixed reference convention, the system must be reversible. Pure name-and-grid systems, like Mapcode , with no way to transform it into a global code, is not a mixed reference, because there is no algorithm to transform the mixed geocode into a grid-based geocode. Geocodes in use and with general scope: Geocodes can be used in place of official street names and/or house numbers , particularly when

1121-412: A more compact form for storage or transmission. Character encodings are representations of textual data. A given character encoding may be associated with a specific character set (the collection of characters which it can represent), though some character sets have multiple character encodings and vice versa. Character encodings may be broadly grouped according to the number of bytes required to represent

1180-426: A new local grid, in a recurring process . In the illustrated example, the cell TQ 2980 is a sub-cell of TQ 29 , that is a sub-cell of TQ . A system of geographic regular grid references is the base of a hierarchical geocode system . Two geocodes of a hierarchical geocode grid system can use the prefix rule: geocodes with same prefix represents different parts of the same broader location . Using again

1239-449: A parent-child relations, through a well-defined syntactic scheme, the geocode set configures a hierarchical system. A geocode fragment (associated to a subdivision name) can be an abbreviation, numeric or alphanumeric code. A popular example is the ISO 3166-2 geocode system, representing country names and the names of respective administrative subdivisions separated by hyphen. For example DE

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1298-655: A single character: there are single-byte encodings, multibyte (also called wide) encodings, and variable-width (also called variable-length) encodings. The earliest character encodings were single-byte, the best-known example of which is ASCII . ASCII remains in use today, for example in HTTP headers . However, single-byte encodings cannot model character sets with more than 256 characters. Scripts that require large character sets such as Chinese, Japanese and Korean must be represented with multibyte encodings. Early multibyte encodings were fixed-length, meaning that although each character

1357-411: A skunk!"), or AYYLU ("Not clearly coded, repeat more clearly."). Code words were chosen for various reasons: length , pronounceability , etc. Meanings were chosen to fit perceived needs: commercial negotiations, military terms for military codes, diplomatic terms for diplomatic codes, any and all of the preceding for espionage codes. Codebooks and codebook publishers proliferated, including one run as

1416-419: A suitable sufficiently close locality. When the mixed reference is also short (9 characters in the second example) and there are a syntax convention to express it (suppose  CP‑PR~bgxed ), this convention is generating a new name-and-grid geocode system . This is not the case of the first example because, strictly speaking, "Cape Verde, Praia" is not a code. To be both, a name-and-grid system and also

1475-433: A syntactical partition, where for example the first part (code prefix) is a name-code and the other part (code suffix) is a grid-code. Example: For mnemonic coherent semantics, in fine-grained geocode applications, the mixed solutions are most suitable. Any geocode system based on regular grid , in general is also a shorter way to express a latitudinal/longitudinal coordinate. But a geocode with more than 6 characters

1534-454: A toponym and "an unambiguous spatial footprint of the same place". Any standardized system of toponym resolution, having codes or encoded abbreviations, can be used as geocode system . The "resolver" agent in this context is also a geocoder . Sometimes names are translated into numeric codes, to be compact or machine-readable. Since numbers, in this case, are name identifiers, we can consider "numeric names" — so this set of codes will be

1593-403: Is Germany , a simple geocode, and its subdivisions (illustrated) are DE-BW for Baden-Württemberg , DE-BY for Bayern , ..., DE-NW for Nordrhein-Westfalen , etc. The scope is only the first level of the hierarchy. For more levels there are other conventions, like HASC code. The HASC codes are alphabetic and its fragments have constant length (2 letters). Examples: Two geocodes of

1652-473: Is a numeric representation of basin names in a hierarchical syntax schema (first level illustred). For example, the HUC 17 is the identifier of " Pacific Northwest Columbia basin "; HUC 1706 of " Lower Snake basin ", a spatial subset of HUC 17 and a superset of 17060102 ("Imnaha River"). Inspired in the classic alphanumeric grids , a discrete global grid ( DGG ) is a regular mosaic which covers

1711-413: Is a system of rules to convert information —such as a letter , word , sound, image, or gesture —into another form, sometimes shortened or secret , for communication through a communication channel or storage in a storage medium . An early example is an invention of language , which enabled a person, through speech , to communicate what they thought, saw, heard, or felt to others. But speech limits

1770-473: Is capable of covering all points with latitudes ranging from 40°N to 80°N and longitudes from 48°W to 144°W , as well as all points with latitudes ranging from 80°N to 88°N and longitudes from 56°W to 136°W . Each National Tiling System zone is divided into individual 1:1,000,000 scale "map series", denoted by a number indicating its general position in the country (e.g., 30 ); which each map series divided into several 1:250,000 scale "map areas", denoted by

1829-414: Is difficult for remember. On the other hand, a geocode based on standard name (or abbreviation or the complete name) is easier to remember. This suggests that a "mixed code" can solve the problem, reducing the number of characters when a name can be used as the "context" for the grid-based geocode. For example, in a book where the author says "all geocodes here are contextualized by the chapter's city". In

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1888-497: Is known as the National Tiling System , which also functions as a coarse method of geocoding . This scheme initially splits the country into three major "zones", each spanning a different range of latitudes. The "Southern zone" covers latitudes between 40°N and 68°N , the "Arctic zone" covers latitudes between 68°N and 80°N , and the "High Arctic zone" covers latitudes between 80°N and 88°N . The National Tiling System

1947-525: Is the most known algorithm for deriving prefix codes. Prefix codes are widely referred to as "Huffman codes" even when the code was not produced by a Huffman algorithm. Other examples of prefix codes are country calling codes , the country and publisher parts of ISBNs , and the Secondary Synchronization Codes used in the UMTS WCDMA 3G Wireless Standard. Kraft's inequality characterizes

2006-611: The Unicode character set; UTF-8 is the most common encoding of text media on the Internet. Biological organisms contain genetic material that is used to control their function and development. This is DNA , which contains units named genes from which messenger RNA is derived. This in turn produces proteins through a genetic code in which a series of triplets ( codons ) of four possible nucleotides can be translated into one of twenty possible amino acids . A sequence of codons results in

2065-415: The 1960s to about 1975, then abandoned, and liquidated in the 1980s (along with the scattered coverage of the 1:500,000 and 1:125,000 scale). Most were quadrangles of 7.5' by 7.5', but two unusually-shaped coverages were provided to cover Whitehorse, one being primarily 105 D/11 h but with portions of g and 105 D/10 e; the other had small portions of 105 D/14 a and b. "Military Town Plans" were also prepared on

2124-516: The Southern zone, map series are divided into sixteen map areas, each assigned a letter from A through P, while in the Arctic and High Arctic zones, they are split into eight map areas, each assigned a letter from A through H. The letters are assigned in a boustrophedon pattern starting with the southeasternmost map area in a series. Each map area in turn is split into sixteen map sheets, numbered from 1 through 16 in an identical boustrophedon pattern to

2183-446: The case of OLC there is a second key schema, after the + separator: 58PJ642P+48 is the key 2 of the cell  58PJ642P+4 . It uses two key schemas. Some geocodes systems (e.g. S2 geometry) also use initial prefix with non-hierarchical key schema. In general, as technical and non-compact optional representation, geocode systems (based on hierarchical grids) also offer the possibility of expressing their cell identifier with

2242-425: The cell ID is standardized, it becomes a geocode. Geocodes of different geocode systems can represent the same position in the globe, with same shape and precision, but differ in string -length, digit-alphabet, separators, etc. Non-global grids also differ by scope, and in general are geometrically optimized (avoid overlaps, gaps or loss of uniformity) for the local use. Each cell of a grid can be transformed into

2301-448: The chapter about Paris, where all places have a Geohash with prefix u09 , that code can be removed —. For instance Geohash u09tut can be reduced to tut , or, by an explicit code for context "FR-Paris tut ". This is only possible when the context resolution (e.g. translation from "FR-Paris" to the prefix u09 ) is well-known. In fact a methodology exists for hierarchical grid-based geocodes with non-variable size, where

2360-473: The code prefix describes a broader area, which can be associated with a name. So, it is possible to shorten by replacing the prefix to the associated context. The most usual context is an official name. Examples: The examples of the Mixed reference column are significantly easier than remembering DGG code column. The methods vary, for example OLC can be shortened by elimination of its first four digits and attaching

2419-404: The confidentiality of communications, although ciphers are now used instead. Secret codes intended to obscure the real messages, ranging from serious (mainly espionage in military, diplomacy, business, etc.) to trivial (romance, games) can be any kind of imaginative encoding: flowers , game cards, clothes, fans, hats, melodies, birds, etc., in which the sole requirement is the pre-agreement on

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2478-491: The encoded strings. Before giving a mathematically precise definition, this is a brief example. The mapping is a code, whose source alphabet is the set { a , b , c } {\displaystyle \{a,b,c\}} and whose target alphabet is the set { 0 , 1 } {\displaystyle \{0,1\}} . Using the extension of the code, the encoded string 0011001 can be grouped into codewords as 0 011 0 01, and these in turn can be decoded to

2537-423: The entire Earth's surface (the globe). The regularity of the mosaic is defined by the use of cells of same shape in all the grid, or "near the same shape and near same area" in a region of interest, like a country. All cells of the grid have an identifier (DGG's cell ID), and the center of the cell can be used as reference for cell ID conversion into geographical point. When a compact human-readable expression of

2596-417: The geocode can also be translated between human-readable (e.g. hexadecimal ) and internal (e.g. binary 64-bit unsigned integer ) representations. Geocodes like country codes , city codes, etc. comes from a table of official names, and the corresponding official codes and geometries (typically polygon of administrative areas). "Official" in the context of control and consensus, typically a table controlled by

2655-442: The geocodes are also components of the system definition: Many syntax and semantic characteristics are also summarized by classification. Any geocode can be translated from a formal (and expanded) expression of the geographical entity, or vice versa, the geocode translated to entity. The first is named encode process, the second decode . The actors and process involved, as defined by OGC , are: In spatial indexing applications

2714-425: The infantry on the battlefield, etc. Communication systems for sensory impairments, such as sign language for deaf people and braille for blind people, are based on movement or tactile codes. Musical scores are the most common way to encode music . Specific games have their own code systems to record the matches, e.g. chess notation . In the history of cryptography , codes were once common for ensuring

2773-486: The latter area does not contain enough land in Canada to warrant a separate printing. Geocode A geocode is a code that represents a geographic entity ( location or object ). It is a unique identifier of the entity, to distinguish it from others in a finite set of geographic entities. In general the geocode is a human-readable and short identifier. Typical geocodes and entities represented by it: The ISO 19112:2019 standard (section 3.1.2) adopted

2832-440: The map areas. A map sheet in the Southern zone spans half a degree of longitude, one in the Arctic zone spans a full degree, and one in the High Arctic zone spans two degrees. Each of these 1:50,000 sheets, in turn, was at one time split into eight 1:25,000 scale map sub-sheets, lettered as lower-case a to h, using the same boustrophedon pattern as the smaller-scale map areas and sheets. These 1:25,000 scale maps were produced from

2891-497: The map sheet designator. All map series span four degrees of latitude, but each spans a different range of longitudes depending on the zone it is located in. Map series in the Southern and Arctic zones span eight degrees of longitude, while those in the High Arctic zone span sixteen degrees of longitude. In the Southern and Arctic zones, the National Tiling System numbers map series by latitude and longitude. After padding

2950-472: The meaning by both the sender and the receiver. Other examples of encoding include: Other examples of decoding include: Acronyms and abbreviations can be considered codes, and in a sense, all languages and writing systems are codes for human thought. International Air Transport Association airport codes are three-letter codes used to designate airports and used for bag tags . Station codes are similarly used on railways but are usually national, so

3009-415: The nominal value of the electrical resistors or that of the trashcans devoted to specific types of garbage (paper, glass, organic, etc.). In marketing , coupon codes can be used for a financial discount or rebate when purchasing a product from a (usual internet) retailer. In military environments, specific sounds with the cornet are used for different uses: to mark some moments of the day, to command

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3068-452: The range of communication to the distance a voice can carry and limits the audience to those present when the speech is uttered. The invention of writing , which converted spoken language into visual symbols , extended the range of communication across space and time . The process of encoding converts information from a source into symbols for communication or storage. Decoding is the reverse process, converting code symbols back into

3127-435: The same 1:25,000 scale, with "declassified versions" available to the public; the classified versions had places of military significance marked; these maps did not follow a quadrangle plan of any kind. Not all National Topographic System maps strictly follow the National Tiling System's linear grid. Some maps also, as an "overedge", cover land in an area which would otherwise be covered by an adjacent map sheet, simply because

3186-530: The same information to be sent with fewer characters , more quickly, and less expensively. Codes can be used for brevity. When telegraph messages were the state of the art in rapid long-distance communication, elaborate systems of commercial codes that encoded complete phrases into single mouths (commonly five-minute groups) were developed, so that telegraphers became conversant with such "words" as BYOXO ("Are you trying to weasel out of our deal?"), LIOUY ("Why do you not answer my question?"), BMULD ("You're

3245-409: The sequence of source symbols acab . Using terms from formal language theory , the precise mathematical definition of this concept is as follows: let S and T be two finite sets, called the source and target alphabets , respectively. A code C : S → T ∗ {\displaystyle C:\,S\to T^{*}} is a total function mapping each symbol from S to

3304-798: The sets of codeword lengths that are possible in a prefix code. Virtually any uniquely decodable one-to-many code, not necessarily a prefix one, must satisfy Kraft's inequality. Codes may also be used to represent data in a way more resistant to errors in transmission or storage. This so-called error-correcting code works by including carefully crafted redundancy with the stored (or transmitted) data. Examples include Hamming codes , Reed–Solomon , Reed–Muller , Walsh–Hadamard , Bose–Chaudhuri–Hochquenghem , Turbo , Golay , algebraic geometry codes , low-density parity-check codes , and space–time codes . Error detecting codes can be optimised to detect burst errors , or random errors . A cable code replaces words (e.g. ship or invoice ) with shorter words, allowing

3363-437: The side illustration: TQ 28 and TQ 61 represents geographically interior parts of TQ , the common prefix. Hierarchical geocode can be split into keys. The Geohash 6vd23gq is the key q of the cell 6vd23g , that is a cell of 6vd23 (key g ), and so on, per-digit keys. The OLC 58PJ642P is the key 48 of the cell 58PJ64 , that is a cell of 58Q8 (key 48 ), and so on, two-digit keys. In

3422-407: The term "geographic identifier" instead geocode, to encompass long labels: spatial reference in the form of a label or code that identifies a location . For example, for ISO, the country name “People's Republic of China” is a label. Geocodes are mainly used (in general as an atomic data type ) for labelling , data integrity , geotagging and spatial indexing . In theoretical computer science

3481-500: Was represented by more than one byte, all characters used the same number of bytes ("word length"), making them suitable for decoding with a lookup table. The final group, variable-width encodings, is a subset of multibyte encodings. These use more complex encoding and decoding logic to efficiently represent large character sets while keeping the representations of more commonly used characters shorter or maintaining backward compatibility properties. This group includes UTF-8 , an encoding of

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