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Location Proofs

A location proof couples a location claim with location evidence supporting that claim. It provides independently evaluable evidence about how well the claim corresponds to physical reality — not a guarantee that it does. The key aim is to raise the cost of lying about where things happen, so we can build more interesting applications on more credible spatial facts. Astral’s Location Proof Framework provides a library of location proof plugins that collect evidence from different systems and compose them in a way that can be parsed and verified. We are building to support the widest possible range of ways to verify location — we don’t want to make assumptions about what forms of evidence system designers will or won’t accept. One of the framework’s central ideas is composability: multi-factor location proofs that bundle evidence collected from independent proof-of-location systems into a single verifiable artifact.

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Why Location Proofs Matter

Most location data today is self-reported. A device says “I’m at these coordinates” and the receiving system takes it on faith. This works until the stakes are high enough to justify forgery — and the cost of forging GPS coordinates is essentially zero. Location proofs change the economics. By requiring evidence from independent proof-of-location systems, they raise the cost of forgery. The goal is not absolute certainty (which we believe is not achievable for physical location), but making the cost of a convincing forgery exceed the value of the fraud.

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The Certainty Spectrum

Not all location proofs are equally strong. The level of assurance depends on the number, diversity, and quality of the evidence sources. To reason about the relative security of location proofs, we are developing a 5-level certainty spectrum: Most real-world applications today operate at L1 or L2. Higher levels require proof-of-location systems that don’t yet exist at scale — this is an active area of research.

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Design Principles

No one-size-fits-all. Different applications need different levels of assurance. A social check-in app has different requirements than a land title registry. Location proofs are designed to be composable so applications can choose the right level for their use case. Neutral framework. Astral provides the structure for collecting, composing, and evaluating location evidence — not opinions about which evidence sources to trust. Some applications will accept government-issued attestations as sufficient; others will give them no weight. The framework accommodates both without preference. Probabilistic, not deterministic. Location proofs produce credibility scores, not binary verdicts. The evidence either supports the claim strongly, weakly, or not at all — and applications decide what threshold they need. Compose for the use case. A single location stamp from one proof-of-location system coupled with a claim is a valid location proof. Multiple location stamps from independent systems are stronger. The architecture supports both without requiring a minimum. Information monotonicity. Adding valid, independent evidence may push confidence in the claim up or down, but it should always sharpen the picture: you end up more sure of where the claim really stands, even when that turns out to be unfavorable. More evidence should never leave you more confused. Verifiability throughout. Location stamps should be cryptographically signed, evidence bundles should maintain clear provenance, and evaluation functions should be identifiable. Every layer of the location proof should be independently checkable. Forgery cost principle. The cost of forging a location proof should exceed the economic value of the transaction it underpins. A $10 check-in reward needs less forgery resistance than a $10M land title transfer.

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The Location Proof Pipeline

Location proofs are built from a series of concepts that compose together:

1. Proof-of-location systems — The technical and social systems that produce location evidence
2. Location stamps — Individual pieces of evidence from a single proof-of-location system
3. Location claims — Assertions about where and when an event occurred
4. Composing location proofs — Bundling location stamps with a location claim into a verifiable artifact
5. Location proof evaluation — How Astral assesses the credibility of a location proof

Each of the following pages covers one of these concepts in detail.

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See also:

• SDK: Location proofs — creating, signing, and verifying location proofs
• Plugins overview — the location proof plugin ecosystem