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Location Stamps

A location stamp is a signed piece of evidence from a single proof-of-location system about an observed location. It’s the atomic unit of location evidence in Astral — the building block from which the location evidence component of a location proof is composed.

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Location Stamp Contents

Conceptually, a location stamp carries four things: Observed location. Where the proof-of-location system’s evidence indicates the subject was. This uses the same Location Protocol v0.2 format as location records — a geometry with a spatial reference system. Temporal footprint. When the observation was made. Both location stamps and location claims use time ranges (start and end), not single instants — observations take time, and evidence may span a window. Plugin identification. Which location proof plugin + version was used to create this evidence. This is necessary for verification — the verifier needs to know what kind of evidence to expect and how to evaluate it. Signals and signatures. The raw evidence data (signals) collected by the proof-of-location system, plus cryptographic signatures that bind the evidence to its source. The signals are plugin-specific — each proof-of-location system produces different kinds of raw data (sensor readings, latency measurements, attestation tokens, etc.).

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Independence From Claims

This is a key design decision. A location stamp says “here is evidence about an observed location” — it does not say “this evidence supports a particular claim.” The separation matters because:
  • The same location stamp could be evaluated against different location claims
  • Location stamps can be collected before a location claim is formulated
  • Verification can assess each location stamp on its own merits before comparing it to the claim
The connection between location stamps and location claims happens at the location proof level, where they’re bundled together. The evaluation process then assesses whether the observed evidence (from location stamps) support the asserted location (from the location claim).

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Internal validity

Each location stamp carries enough information to verify its own internal validity — independent of any location claim. Stamp verification checks:
  • Signatures — Are the cryptographic signatures valid? Do they chain back to a trusted source?
  • Structure — Does the location stamp conform to the expected format for its plugin?
  • Signal consistency — Are the raw signals internally consistent? (e.g., do multiple sensor readings agree?)
This is the first phase of location proof evaluation — checking each location stamp before assessing how well it supports the claim.

Next: Location claims

Assertions about where and when an event occurred
See also: