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Geohashing

Geohashing is an outdoor recreational activity and spontaneous adventure game in which participants travel to a randomly generated geographic coordinate, determined daily by a hashing algorithm, to explore, document their expedition, and often meet others at the site.^[1]^[2] The game divides the world into 1°×1° latitude-longitude graticules, generating a unique point within each, with players typically targeting the nearest one to their location or the single daily "globalhash."^[1]^[3] Invented by webcomic artist Randall Munroe as a humorous concept in xkcd comic #426, published on May 21, 2008, geohashing quickly evolved from a satirical idea into a global pursuit with a dedicated community.^[2]^[3] The algorithm employs the opening value of the Dow Jones Industrial Average stock index, combined with the date, to produce pseudorandom coordinates that remain unpredictable beyond a short advance period, ensuring spontaneity and preventing overplanning.^[3] Since its inception, participants have completed over 19,000 documented expeditions worldwide as of November 2025, fostering a decentralized network without formal organization.^[4] Key features include achievement systems for milestones like reaching multiple sites or venturing into challenging terrains, with official meetups commonly held on Saturdays at 16:00 local time to encourage social interaction.^[1] The activity emphasizes safety, legality, and environmental respect, with the globalhash often falling in remote or oceanic areas, adding elements of rarity and adventure—such as a notable 2012 expedition near the South Pole.^[1]^[3] Documentation occurs via a community wiki supporting multiple languages, preserving stories, photos, and GPS proofs from diverse locations.^[1]

Overview

Definition and Purpose

Geohashing is an outdoor recreational activity invented by Randall Munroe on May 21, 2008, through an xkcd webcomic, in which participants travel to a specific latitude and longitude coordinate generated algorithmically from the current date and the opening value of the Dow Jones Industrial Average.^[2]^[5] The activity divides the world into 1°×1° graticules, with a unique "hashpoint" calculated daily for each, encouraging individuals to venture to the nearest accessible point within their region.^[1] The primary purpose of geohashing is to foster spontaneous exploration of local environments, promote social interactions among participants who may be strangers, and embrace algorithmic serendipity by turning pseudorandom coordinates into real-world adventures.^[5]^[1] Unlike geocaching, which involves seeking pre-placed physical caches, geohashing has no hidden objects; instead, reaching the hashpoint itself—often in parks, fields, or urban spots—serves as the goal, with optional documentation of the journey through photos or stories.^[1] Daily hashpoints act as natural focal points for meetups, particularly on Saturdays at 4:00 p.m. local time, helping to build a global community of enthusiasts known as "hashers" who have completed over 18,000 expeditions since the activity's inception as of 2023.^[5]^[1] This structure cultivates serendipitous connections and shared narratives, turning solitary outings into collaborative experiences across diverse locations worldwide.^[1]

Core Principles

Geohashing operates on the principle of algorithmic determinism, where daily hashpoints are generated through a pseudorandom process that relies on the current date and the Dow Jones Industrial Average opening price, ensuring that the resulting coordinates are reproducible and fair for all participants worldwide.^[6] This method uses the MD5 hashing algorithm to transform the date and stock price into a hexadecimal string, which is then converted into latitude and longitude offsets within predefined 1°×1° graticules, preventing any individual from influencing the location and promoting equal opportunity for adventure.^[6] The pseudorandom nature, while appearing random, is fully deterministic given the inputs, allowing anyone to verify the coordinates independently without reliance on centralized authority.^[1] Participation in Geohashing is entirely voluntary and designed with low barriers to entry, requiring no formal registration or membership to join expeditions.^[1] Individuals self-identify as participants by documenting their experiences on communal online wikis or forums, fostering a decentralized community where over 18,000 expeditions have been recorded since 2008 as of 2023.^[1] This open structure encourages spontaneous involvement from anyone interested in exploration, with tools like coordinate calculators available freely to compute hashpoints.^[1] At its core, Geohashing upholds a social contract centered on safety, consent, and enjoyment, with explicit guidelines to prioritize participant well-being over reaching any location.^[7] Participants are instructed to avoid dangerous, inaccessible, or illegal sites, and to respect property owners by leaving immediately if requested, ensuring all interactions remain consensual and non-confrontational.^[7] The game eschews competitive scoring or rankings in its fundamental rules, instead emphasizing collaborative fun and goodwill, such as environmental stewardship during visits, though optional extensions may introduce personal challenges.^[7] This ethos reinforces Geohashing as a lighthearted pursuit of serendipitous discovery rather than a structured contest.^[1]

Geohash Encoding

Coordinate Encoding Process

In the geohashing game, the "encoding" refers to the algorithmic process of generating daily hashpoint coordinates within each 1°×1° graticule using a deterministic pseudorandom method based on the date and the Dow Jones Industrial Average (DJIA) opening value. This ensures unpredictability until the DJIA is available, typically after the market opens. The process does not involve encoding existing coordinates into strings but rather computing new coordinates from hashed inputs.^[6] The inputs are the date GD in YYYY-MM-DD format and the DJIA opening value DJOD for the applicable trading day, adjusted by the 30W time zone rule: for graticules west of -30° longitude, use the latest DJOD up to GD (e.g., previous Friday for weekends); for those east, use the latest up to GD - 1 day. These are concatenated as a string, e.g., "2025-11-16-42000.50" for a hypothetical date.^[6]^[8] An MD5 hash is computed on this string, producing a 32-character hexadecimal digest (128 bits). The hash is split into two 16-character halves. A decimal point is prepended to each half to form hexadecimal fractions between 0 and 1, e.g., 0.db9318c2259923d0 and 0.e4bb40c... . These are converted to decimal fractions f_\phi and f_\lambda, each with approximately 64 bits of precision.^[6] For a given graticule defined by integer latitude \phi_g \in [-90, 90) and longitude \lambda_g \in [-180, 180), the hashpoint coordinates are:

\phi = \phi_g + f_\phi, \quad \lambda = \lambda_g + f_\lambda

where the fractions are scaled to the 1° range of the graticule, yielding \phi \in [\phi_g, \phi_g + 1) and \lambda \in [\lambda_g, \lambda_g + 1). This produces a unique point per graticule daily, with the globalhash using the [0,0] graticule. For example, on 2008-05-21 (the comic's date), the [37,-122] graticule (near xkcd's origin) yields approximately 37.419215, -122.177121.^[6]^[2] Coordinates are typically represented in decimal degrees for documentation, without conversion to compact strings like base-32 Geohash (a separate system). The precision from the 64-bit fractions is theoretically about $10^{-19} degrees (sub-atomic scales), but practically limited by GPS accuracy to 1-10 meters.^[6]

Precision and Grid Structure

The geohashing grid is composed of 33,110 graticules, each a 1°×1° cell in latitude-longitude space, covering the world from -90° to 90° latitude and -180° to 180° longitude (excluding poles beyond 89°-91° for practicality). Unlike hierarchical systems, graticules are fixed and non-overlapping, with hashpoints uniformly distributed within each via the hash fraction. This structure preserves global coverage while localizing adventures to nearby areas.^[1]^[6] Graticule dimensions vary due to Earth's sphericity: latitude intervals are consistently ~111 km per degree, while longitude intervals are ~111 km × \cos(\phi) , shrinking to near zero at the poles. For example, at the equator, a graticule spans ~111 km × 111 km; at 60° latitude, ~111 km × 55.6 km. Hashpoints within graticules add no further subdivision but provide high internal precision.^[9] The system's precision ensures points are unpredictable yet verifiable, with no need for variable-length encoding. In practice, expeditions use GPS devices or apps to navigate to the exact coordinates, documenting success within ~5 km (a "success" threshold for remote areas). No formal table of precisions exists, as the grid is coarse (graticule-scale) with fine point resolution.^[1]

Generating Hashpoints

Algorithm Mechanics

The geohashing algorithm derives a unique daily hashpoint within a specified 1° × 1° graticule by hashing a concatenation of the date and the Dow Jones Industrial Average (DJIA) opening value using the MD5 cryptographic function. The graticule is determined by the floor values of the chosen location's latitude and longitude, providing the base integer degrees for the computation. This ensures that the resulting point lies within a local geographic cell relative to the user's area.^[2]^[6] To prepare the input, the date is formatted as YYYY-MM-DD, and the DJIA opening value is selected according to the 30° W time zone rule: for graticules west of 30° W longitude, it uses the opening on the geohashing date or the most recent trading day; east of 30° W, it uses the prior day's value to synchronize with market hours. These elements are concatenated with a hyphen, such as "2025-11-13-42500.25", where the DJIA value includes its decimal places as published. This string is then processed through the MD5 algorithm to produce a 128-bit hash represented as a 32-character hexadecimal string.^[10] The hash is divided into two 16-character hexadecimal segments: the first for the latitude offset and the second for the longitude offset. Each segment is converted to a fractional value by interpreting it as a hexadecimal fraction—prepending "0." to the digits—and then transforming it to decimal, yielding a value f where $0 \leq f < 1. Equivalently, this can be computed by converting the hexadecimal to its 64-bit binary representation and dividing the integer value by $2^{64}. The final coordinates are obtained by adding these fractions to the graticule's base degrees:

\text{latitude} = \lfloor \text{base latitude} \rfloor + f_{\text{lat}}

\text{longitude} = \lfloor \text{base longitude} \rfloor + f_{\text{lon}}

This scaling confines the hashpoint to the graticule while providing pseudo-random distribution within it, with precision up to approximately 10^{-5} degrees when using four decimal places in practice.^[6]^[2] If the computed hashpoint lands in an ocean or otherwise inaccessible area, such as private property or dangerous terrain, the official guidelines advise against attempting to reach it, emphasizing safety and legality. In community practice, participants often "punt" by targeting the nearest accessible land point within the graticule to still claim the expedition.^[1]

Date and Location Inputs

In geohashing, the date input is the current date expressed in Coordinated Universal Time (UTC) and formatted as YYYY-MM-DD, which serves as the primary temporal component for generating daily hashpoints.^[2] This ensures a consistent global reference point, with the date "frozen" for historical or challenge-based events, such as retro geohashing expeditions that recreate coordinates from past dates to commemorate milestones like birthdays.^[11] The use of a frozen date allows participants to target specific historical locations without altering the core algorithm, maintaining verifiability through archived Dow Jones Industrial Average (DJIA) opening prices associated with that day.^[5] The location input is determined by the participant's selected graticule, defined as a 1° latitude by 1° longitude block on Earth's surface, which personalizes the hashpoint to a regional scale and permits multiple distinct points per day across different graticules worldwide. The participant chooses a graticule, typically their home one, and the global fractional offsets produced by the daily hash are added to its base integer latitude and longitude, ensuring the resulting point falls within that specific block and encouraging localized exploration.^[2]^[6] International time zones can slightly shift hashpoints by influencing the selection of the DJIA opening value—regions east of 30° W longitude use the prior day's price to account for market timing, preventing premature revelation of coordinates and aligning availability across the globe.^[12]

Participation Rules

Basic Meetup Guidelines

Participating in a geohashing expedition involves a series of straightforward steps to locate and reach the daily hashpoint, a randomly generated coordinate based on the date and a regional graticule.^[13] The process emphasizes exploration while prioritizing safety and legal compliance. To begin, calculate the hashpoint coordinates using online tools such as geohashing.info, which displays daily points on an interactive map, or community-developed scripts and libraries.^[13] For scripting, Python implementations like geohashing.py or the xkcd.geohash package allow users to compute coordinates programmatically from date and graticule inputs.^[14] Once obtained, plan the travel route by examining maps to assess accessibility, terrain, and potential obstacles, ensuring alternative paths are available if needed.^[7] Upon arrival, document the journey with GPS readings, photographs, and notes to verify proximity to the coordinates.^[13] Success is achieved by reaching as close as possible to the point, ideally within the GPS device's margin of error—typically a few meters—though no universal distance threshold is enforced beyond demonstrating effort to touch the exact location.^[15] Afterward, share the experience on the geohashing wiki by creating an expedition report using the provided template, which logs details like participants, photos, and outcomes to earn "success" status.^[13] Safety is paramount: research the location thoroughly in advance to avoid hazardous areas, and travel in groups when feasible, especially for Saturday meetups.^[7] Inform others of your plans, carry identification and location details, and strictly avoid trespassing by respecting private property boundaries and local laws on access rights.^[7] If confronted, leave immediately and document the incident without argument.^[7]

Graticule System and Travel

The graticule system in geohashing divides the Earth's surface into a grid of approximately 64,800 rectangular zones, each measuring 1° latitude by 1° longitude, to facilitate organized global participation.^[16] These zones, known as graticules, are identified by their southwest corner coordinates rounded to the nearest whole degree, such as 52, 0 for a region encompassing parts of the Netherlands, Germany, and the North Sea.^[16] Each graticule generates a single, unique hashpoint per day within its boundaries, determined by the algorithm's inputs of date and location, encouraging participants to target points based on their proximity to these defined areas.^[16] The system's structure accounts for varying zone sizes due to Earth's curvature, with equatorial graticules spanning about 111 km north-south and 111 km east-west, while polar ones narrow significantly eastward and westward.^[16] Travel to hashpoints presents diverse logistical challenges, as locations can fall in urban settings, rural landscapes, oceanic expanses, or private property, requiring participants to navigate accessibility constraints.^[17] Common obstacles include international borders that may demand visas or complicate routes, rugged terrain such as rivers or ravines that hinder foot or vehicle access, and adverse weather conditions that affect safety and timing.^[17] For instance, oceanic hashpoints often necessitate boating or are deemed unreachable without specialized equipment, while private land may involve obtaining permissions to avoid trespassing.^[17] Participants must also consider time zones and daylight hours, as hashpoints are valid only until midnight local time at the location.^[17] Regional conventions enhance the graticule framework by recognizing milestones in exploration, such as "virgin graticules"—areas where no prior successful expedition has occurred—now formalized as the Graticule Unlocked achievement for the first group to reach a hashpoint there.^[18] This incentivizes ventures into unexplored zones, with documentation required via photos or GPS proof on the community wiki.^[18] For remote or challenging graticules, multi-day expeditions are common, allowing travelers to combine multiple hashpoints across regions during extended trips.^[17] An illustrative contrast is a hashpoint in the Moscow graticule (55, 37), which might involve public transit navigation through city infrastructure, versus a rural point in the U.S. Midwest (e.g., 40, -90), typically reachable by personal vehicle over open roads but potentially impeded by agricultural fields or weather.^[17]

History and Development

Invention by Randall Munroe

Geohashing was invented by Randall Munroe, the creator of the webcomic xkcd, on May 21, 2008, through the publication of comic strip #426 titled "Geohashing."^[2] This strip introduced the concept as a recreational activity designed to generate daily random coordinates worldwide, encouraging participants to travel to these locations for spontaneous exploration and potential meetups.^[5] The invention drew inspiration from the xkcd comic's humorous take on time travel and random events, aiming to transform abstract algorithmic randomness into real-world adventure without the logistical burdens of traditional games like geocaching, such as hiding physical caches or requiring advance registration.^[19] The core motivation behind geohashing was to foster low-commitment, algorithmically determined outings that anyone with access to coordinates could join, promoting serendipitous social interactions while avoiding organized planning or permissions.^[5] Munroe emphasized reachability as a key factor, advising participants to skip points in inaccessible areas like oceans or private property, and suggested meetups on reachable Saturdays at 4:00 p.m. local time.^[2] This approach ensured the activity remained accessible and fun, relying solely on documentation—typically photographs—to verify participation.^[5] Initial implementation centered on the algorithm detailed in the comic, which uses the MD5 hash of a date string combined with the Dow Jones Industrial Average opening price (or the most recent weekday's if unavailable) to derive latitude and longitude values within predefined 1° × 1° graticules covering the globe.^[2] On the day of the comic's release, Munroe's accompanying blog post provided clarifications and linked to an early online coordinate calculator developed by contributor Dan, which visualized points on Google Maps for easy access.^[5] This tool marked the practical starting point for computation, enabling immediate experimentation without custom coding. The first documented expedition occurred on May 24, 2008—the initial Saturday following the invention—near Champaign-Urbana, Illinois, where participants picnicked at the hashpoint approximately 20 miles from the city. Early adoption was swift within the xkcd community, with a dedicated wiki launched concurrently to log expeditions and share photos.^[5] By May 23, 2008, Munroe reported hundreds of wiki users and initial meetups in cities such as Boston, demonstrating the concept's immediate appeal.^[12] By 2009, the activity had expanded internationally, with documented expeditions across multiple continents and refinements to the algorithm for better global equity, such as adjustments to stock price inputs for non-U.S. regions.^[12]

Growth and Community Evolution

Following its introduction in the xkcd comic on May 21, 2008, geohashing quickly gained traction among online enthusiasts, sparking immediate expeditions and community discussions.^[2] The activity's growth accelerated in the subsequent years, with the launch of a dedicated geohashing wiki on the xkcd platform in May 2008 serving as a central hub for documenting expeditions and sharing experiences.^[5] By 2009-2012, participation expanded as users developed supporting tools, including coordinate calculators and achievement systems, fostering a structured yet spontaneous global network.^[3] Technological advancements further propelled accessibility during this period; by 2011, mobile applications like GeoHash for iOS enabled real-time coordinate generation and navigation, drawing in users beyond desktop computing.^[20] Key milestones underscored this momentum: the community surpassed 10,000 documented expeditions by March 2015, coinciding with deeper integration of GPS devices for precise location tracking and social media for meetup coordination.^[21] These developments highlighted geohashing's appeal as a low-barrier adventure generator, blending algorithmic randomness with real-world exploration.^[3] The community's evolution reflected a transition from a niche pursuit rooted in xkcd's hacker-oriented readership to a wider recreational activity attracting diverse participants interested in outdoor challenges and serendipitous travel.^[3] This shift brought growing pains, such as wiki moderation demands to manage expedition logs and resolve disputes over achievements, culminating in operational challenges like the site's five-month outage from August 2019 to February 2020 due to a server hack.^[22] Following the outage, the community migrated the wiki to an independent site at geohashing.site to ensure long-term stability.^[22] As of 2025, geohashing maintains sustained global activity, with over 18,000 total documented expeditions and ongoing contributions via the revitalized wiki, supported by community-driven server migrations and tool updates.^[1] Annual participation hovers around 500 meetups, reflecting a stable base influenced by post-2020 shifts toward flexible lifestyles that encourage spontaneous outings.^[1]

Community and Impact

Meetup Events and Culture

Geohashing meetups vary in scale and format, ranging from solo expeditions where individuals venture alone to reach the daily coordinate, to larger group gatherings such as picnics organized at accessible hashpoints. Group events often emphasize shared activities, like the Picnic achievement, which recognizes participants who bring food and dine together at the location to enhance the communal experience. For more adventurous participants, multi-graticule tours—known as Graticule Hopper expeditions—involve traveling across multiple one-degree latitude-longitude grids in a single day to hit several hashpoints, sometimes covering hundreds of miles and requiring coordinated planning among participants.^[23]^[24] The culture of geohashing draws heavily from its xkcd origins, infusing events with humor and whimsy, such as the tradition of "munching" where participants eat snacks or meals precisely at the hashpoint to commemorate their arrival. This lighthearted approach extends to playful achievements like the Buccaneer Geohash, encouraging costume elements like pirate attire for added fun during meetups. A core cultural practice is storytelling through detailed expedition reports posted on the community wiki, where hashers document their journeys, challenges, and discoveries, fostering a shared narrative tradition that builds camaraderie among global participants. Post-meetup rituals typically include group photos at the exact coordinates, often earning the Star Photographer achievement for those who capture and share high-quality images of the event.^[2]^[25]^[17]^[26] Geohashing promotes inclusivity by welcoming participants of all skill levels, from novice explorers to seasoned travelers, with no formal barriers to entry beyond reaching the point. The activity's serendipitous nature allows for meaningful interactions with fellow hashers or even non-participants, as long as exchanges go beyond brief greetings, contributing to the Meet-up achievement that celebrates these social encounters. This emphasis on connection has led to lasting real-world friendships and collaborative travel adventures, as hashers coordinate across distances to join expeditions and share experiences through tools like the Meetup Graph, which visualizes interpersonal networks within the community.^[27]^[28]

Achievements and Variations

Geohashing participants have documented numerous achievements that highlight dedication, exploration, and ingenuity within the game's framework. Regional achievements recognize those who have successfully reached geohash points in every possible graticule containing land within a specific political division, such as completing all 11 graticules in Brandenburg, Germany, by user relet.^[29] These feats demonstrate sustained effort across geographic boundaries, with smaller regions like Rhode Island (spanning two graticules) serving as accessible entry points, while larger areas like U.S. states pose greater challenges due to multiple graticules per state.^[29] Personal milestones include the xkcd centurion achievement, awarded for reaching 100 geohashes specifically on Saturdays at 4 p.m., symbolizing commitment to the game's traditional meetup time.^[11] Extreme expeditions underscore the game's adventurous spirit, with polar ventures representing some of the most demanding accomplishments. For instance, a 2012 expedition reached coordinates at 78°N, 15°E in Arctic conditions, accessed by a short walk using spiked soles amid unusually warm, rainy weather that caused icy terrain.^[30] Such efforts align with broader extreme achievements, including the furthest north or south geohash, often claimed in polar-adjacent graticules where environmental hazards amplify the challenge.^[11] Multi-geohash records further exemplify scale, with the highest verified count of 11 successful hashes in a single day achieved by participants Micsnare, Crankl, and B2c on August 2, 2015, involving coordinated travel across multiple locations.^[31] The community continues to thrive, with expeditions ongoing as of 2025, including remarkable coordinated efforts like nine separate expeditions reaching the same point without intersecting in 2024.^[32] Player-created variations extend the standard rules, fostering creativity without altering the core algorithm. Retrohashing involves visiting coordinates generated for dates other than the current day, often to revisit historical points or celebrate personal events like birthdays, using tools such as the Peeron map for calculation while adhering to time zone adjustments post-2008.^[33] This mode allows flexibility for inaccessible current hashes, with expeditions documented by the original date (e.g., 2005-05-26 37 -122 from the xkcd comic) and marked as retro to distinguish them from standard logs.^[33] Community-driven additions, proposed and refined through forums, include themed challenges like costume-based meets or endurance series, ensuring organic evolution guided by collective input rather than central authority.^[11]

References

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A webcomic of romance, sarcasm, math, and language. What is this about? See the wiki. Geohashing Geohashing Permanent link to this comic.Missing: origin | Show results with:origin
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### Summary of Participation Rules and Social Contract Aspects
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### Step-by-Step Instructions for Geohashing
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A python script that can calculate geohash coordinates, given a graticule. It can calculate globalhashes as well. It is meant to be used from the command line, ...
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### Success Criteria for Geohashing Meetups
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### Summary of Graticule System in Geohashing
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