> ## Documentation Index
> Fetch the complete documentation index at: https://astral-6ef288be-docs-policy-evaluation-framing.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Composing Location Proofs

> Bundling location stamps with a location claim into a verifiable artifact

<Note>**Research Preview** — APIs may change. [GitHub](https://github.com/AstralProtocol)</Note>

# Composing Location Proofs

A location proof bundles one or more [location stamps](/concepts/location-stamps) with a [location claim](/concepts/location-claims). It's the verifiable artifact — a claim paired with its supporting evidence.

## Structure

A location proof contains:

* **One location claim** — the assertion being made (where, when, who, what event)
* **One or more location stamps** — evidence from proof-of-location systems

That's it. The simplicity is intentional. A location proof is a container that brings together the assertion and the evidence so they can be [evaluated](/concepts/location-proof-evaluation) together.

## Single-Stamp vs. Multi-Stamp Location Proofs

A location proof with a single location stamp is valid. It represents evidence from one proof-of-location system supporting one location claim. The evaluation can still assess the location stamp's internal validity and how well it supports the claim.

Multi-stamp location proofs from independent proof-of-location systems are stronger. When evidence from unrelated sources agrees, the cost of forgery rises sharply — an attacker would need to simultaneously compromise multiple independent systems. This is where cross-correlation adds value: the evaluation assesses how independent the evidence sources actually are.

Redundant location stamps from the *same* proof-of-location system don't meaningfully increase confidence. Cross-correlation looks for independence between sources.

<Info>
  We are building a taxonomy of proof-of-location systems and quantifying these dimensions as an area of active [research](https://github.com/AstralProtocol/research).
</Info>

## Location Proof Plugins

**Location proof plugins** are the abstraction layer that makes composition practical. Each plugin wraps a [proof-of-location system](/concepts/pol-systems) behind a common interface with five standard methods:

1. **Collect** — Gather raw signals from the proof-of-location system
2. **Create** — Process signals into an unsigned location stamp
3. **Sign** — Cryptographically sign the location stamp
4. **Verify** — Check a location stamp's internal validity
5. **Evaluate** — Assess how well a location stamp supports a location claim

This common interface means a developer can compose evidence from multiple proof-of-location systems — and any future system — using the same SDK patterns. The plugin handles the system-specific details; the SDK handles composition and orchestration.

Plugins and their status:

| Plugin                                | Proof-of-location system             | Environment                           | Status                                           |
| ------------------------------------- | ------------------------------------ | ------------------------------------- | ------------------------------------------------ |
| [ProofMode](/plugins/proofmode)       | Device attestation + sensor fusion   | iOS, Android, React Native            | Working — verification implemented (alpha)       |
| [WitnessChain](/plugins/witnesschain) | Infrastructure latency triangulation | Node.js, any HTTP client              | Experimental — interface defined, early verifier |
| [Mock](/plugins/mock)                 | Configurable test evidence           | Any JavaScript/TypeScript environment | Available for testing (client)                   |

The Verify service also includes experimental stamp-verification logic for `gpsd`, `geoclue`, `wifi-mls`, and `ip-geolocation`.

<Tip>
  Different devices and environments suit different plugins. A mobile app might use ProofMode for on-device attestation, while a backend service could use a network-based source like WitnessChain. ProofMode is working today; the others are experimental with interfaces defined — we're keen to develop new ones with partners. See [Plugins](/plugins/overview) for details on each.
</Tip>

## Composing From Multiple Plugins

To create a multi-stamp location proof, collect location stamps from each plugin independently, then bundle them with a single location claim. The location stamps don't need to know about each other — they just provide independent evidence that the evaluation process cross-correlates.

<Card title="Next: Location proof evaluation" icon="magnifying-glass-chart" href="/concepts/location-proof-evaluation">
  How Astral assesses the credibility of a location proof
</Card>

***

**See also:**

* [SDK: Location proofs](/sdk/location-proofs) — creating and composing location proofs
* [Plugins overview](/plugins/overview) — the full plugin ecosystem
* [Build a custom plugin](/plugins/custom) — implementing the plugin interface