computer science

Geohash-36

Geohash-36 is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Geohash-36 rather than just read about it. In short: The Geohash-36 geocode is an open-source compression algorithm for world coordinate data. It was developed as a variation of the OpenPostcode format developed as a candidate geolocation postcode for the Republic of Ireland.

Key takeaways

Geohash-36 belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Geohash-36 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Geohash-36 from memory before moving on to harder problems.

Reference excerpt

The Geohash-36 geocode is an open-source compression algorithm for world coordinate data. It was developed as a variation of the OpenPostcode format developed as a candidate geolocation postcode for the Republic of Ireland. It is calculated differently and uses a more concise base 36 representation rather than other geocodes that adopted base 32. Despite the name, there are no algorithmic (not use Z-order curve) or typological relationship with Geohash. It is a publicity strategy to relate to a popular geocode of base 32. The encode/decode functions are not mathematically-similar to Geohash functions.

Coding Method Designed for URLs and electronic storage and communication rather than human memory and conversation, it is case-sensitive, using a 36 character alphabet: "23456789bBCdDFgGhHjJKlLMnNPqQrRtTVWX". Character Conversion:

Characters are chosen to avoid vowels, vowel-like numbers, character confusion, and to use lowercase characters which are generally distinct from their uppercase equivalents in standard typefaces. The code can be of varying length and thus precision. Each character represents a further subdivision in a 6 by 6 grid - starting at the North-West (top-left) coordinate and continuing, row by row, to the South-East (bottom-right). Neighbouring coordinates have largely similar encodings and generally vary at the rightmost characters only; however extreme edge cases exist where neighbouring coordinates are on opposing sides of a grid division. Codes sort logically but not in ordinary coordinate order. Without vowels, unintended English-language words are avoided that may appear in the original Geohash code. As vowels are not used, an altitude component of encoded meters is optional with a prefixing "A" character (below sea-level prefixed by a lowercase "a"). An optional checksum is represented using the lowercase English alphabet. It confirms the code as a Geohash-36 and provides a check for incorrect or transposed characters. It is calculated as modulus 26 of the sum of each character value (the altitude delimiters of "A" or "a" are valued at zero) multiplied by its position reading from left to right.

Efficiency Compared to storing GPS coordinates using the Decimal datatype in SQL the Geohash-36 does not save significantly on database bytes. Using DECIMAL(8,5) and DECIMAL(7,5) requires 10-bytes and is accurate to about 1.1 metre squared (or better further from the equator). An equivalent 10-bytes of the Geohash-36 code is accurate to approximately a 6th of square meter. The Statue of Liberty, at coordinates 40.689167, −74.044444, is encoded as 9LVB4BH89g-m. The reverse decoding equates to 40.689168, −74.044445. The Shard building, London, at coordinates 51.504444, −0.086667 is encoded as bdrdC26BqH-m (decodes to 51.504444, −0.086666), or may be successfully shorted to bdrdC26B.

Implementations

C 'libgeohash36' – a pure C implementation of Geohash-36 algorithm.

Ruby 'Geohash36' – a Ruby implementation of the Geohash-36 algorithm.

See also List of geodesic-geocoding systems

References 6.^ "Geohashes" [1]. Retrieved 05 June 2024.

Worked examples

Example 1 — a first encounter with Geohash-36

Start with the simplest possible case. Write down what Geohash-36 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Geohash-36 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Geohash-36 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Geohash-36

In research: Geohash-36 appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Geohash-36 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Geohash-36 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Compression algorithms, Geocodes, so understanding it makes those chapters shorter.
In everyday life: Look for Geohash-36 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Geohash-36 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Geohash-36 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Geohash-36 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Geohash-36 in simple terms?

Why does Geohash-36 matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Geohash-36?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Geohash-36.