# `Geohash`

A rectangle on Earth, as up to 12 letters and digits: `gcpvj0duq`.

Use it to group or look up nearby points by a shared text prefix. For hexagons of near-equal size, use [`H3Cell`](/docs/types/type-h3-cell.md). For an exact position, use [`Point`](/docs/types/type-point.md).

## Shape

One value, held as text in one set form, with no parts: `u09tvw0f6szy`.

## Example

```jadpo
Geohash("gcpvj0duq")
```

`Geohash(raw)` checks the text, and text that isn't one breaks the `format` rule.

`text.parse(raw, as: Geohash)` reads one from text that comes from outside. Text that isn't one at all fails `malformed`, such as `gcpvja`, `GCPVJ` or `gcpvj0duq5x7z`.

## Good to know

- It is lower case, and leaves out `a`, `i`, `l` and `o`, which is how geohashes are written.
- `==` tells you whether two are the same. `<` and `list.sort_by` don't take it.

## In JSON

A string, in a request, a response or `json.write`:

```json
"g"
"gcpvj0duq"
"u09tvw0f6szy"
```

## Details

<details>
<summary>Text form, storage, how it is shown, and operations</summary>

`Geohash` is in the group Geospatial, and has been in Jadpo since 0.1.0.

### Text form

`text.from` writes one standard text form, the same form `text.parse` reads back: `g`, `gcpvj0duq` and `u09tvw0f6szy`.

### How it is stored

It is stored in one column named for the field, of type `text`. `gcpvj0duq` is stored as `'gcpvj0duq'`.

### How it is shown to people

`text.format(value, locale:)` shows it to people in their locale.

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `g` | `g` |
| `gcpvj0duq` | `gcpvj0duq` |
| `u09tvw0f6szy` | `u09tvw0f6szy` |

### Operations

It also takes `text.parse`, `text.from`, `text.format`, `json.read`, `json.write` and `==`. [How every standard type behaves](/docs/every-standard-type-meets-one-contract.md) says how they work.

</details>