# Channels

Public rooms with no owner, no membership list and no moderator. Anyone can join any channel, and joining is just subscribing.

## Two kinds of channel

Every channel is written `#something`. What that something is decides which kind it is:

|  | Geohash channel | Named channel |
| --- | --- | --- |
| Looks like | `#9q5`, `#u4pruy` | `#bitcoin`, `#nymchat` |
| Means | A place | A subject |
| Nostr event kind | `20000`, tagged `['g', geohash]` | `23333`, tagged `['d', channel]` |

Both are ephemeral Nostr events: relays are expected to hold them for a while and drop them, not to archive them forever. Both are also entirely public — unencrypted events that anyone with the relay address can read.

> **Public means public**
>
> Nothing you send to a channel is encrypted, and there is no server you can ask to delete it. Treat a channel post the way you would treat a public forum post that you cannot edit.

## Geohash channels

A [geohash](https://en.wikipedia.org/wiki/Geohash) encodes a latitude and longitude as a short string, where each extra character narrows the area:

| Example | Length | Roughly covers |
| --- | --- | --- |
| `#9` | 1 | A large slice of a continent |
| `#9q` | 2 | A region |
| `#9q5` | 3 | A metropolitan area |
| `#9q5ct` | 5–6 | A neighborhood, then a few streets |

So `#9q5` is "people around Los Angeles" and `#9q5ctr` is a specific corner of it. Shorter prefixes are busier; longer ones are quieter and much more revealing about where you are. This is the same channel scheme [Bitchat](https://bitchat.free) uses, which is part of how the two apps meet.

> **A long geohash is a location disclosure**
>
> Posting in a six-character geohash channel tells everyone reading roughly which few streets you are on. If that matters, use a shorter prefix or a named channel.

## Named channels

Anything that is not a valid geohash is a named channel: `#bitcoin`, `#nymchat`, `#whatever-you-like`. Type `/join #newthing` and if nobody is there, you have made it. There is no registration and no owner — a named channel is simply a tag that clients agree to subscribe to.

## Favorites, sorting and sharing

The channel list has a context menu (the ⋮ on each row) and a header row with search and the globe. From there you can:

- **Favorite** a channel to pin it to the top of the list.
- **Hide** a channel you do not want to see, or **block** it outright — see [Blocking people and channels](https://nymchat.app/docs/moderation/#blocking).
- **Share** it: `/share` produces a link that opens the channel directly.

Four settings shape the list itself, under Settings › Channels:

| Setting | Default | Effect |
| --- | --- | --- |
| Group Chats & PMs Only Mode | Off | Hides geohash channels entirely and skips their subscriptions, which also cuts bandwidth. |
| Sort Geohash Channels by Proximity | Off | Orders them by distance from you. Needs location permission. |
| Default Landing Channel | None | The channel to open on launch. |
| Hide All Non-Favorited Channels | Off | Shows only what you have favorited. |

## The geohash explorer

The globe icon above the channel list opens a world map of where people are actually talking.

![The Nymchat geohash explorer: a world map with green dots marking active geohash channels, and Heat, Day/Night and Geohash controls.](https://nymchat.app/images/docs/globe.webp)

*The geohash explorer. Each dot is an active channel; the buttons along the bottom switch overlays.*

Pan and zoom, and country outlines give way to regions and then cities as you go in. Tap a dot and a panel tells you what the channel is, with a Join button. The controls are:

- **Heat** — shade the map by activity instead of plotting single dots.
- **Day / Night** — overlay the current terminator, so you can see who is awake.
- **Geohash** — draw the geohash grid at a precision matched to the zoom level, which is the quickest way to see what a prefix actually covers.
- A time filter — **1h, 3h, 6h, 12h or 24h** — for how far back "active" reaches.