Global Field ID identifiers

The field identifier is designed to be easy to capture and communicate in both digital and non-digital formats without mistakes

There are multiple types of identifier in the Global FieldID® system:

  • Fields
  • Boundaries
  • Boundary References

In addition, third party cross-references have their own identifiers.

Field Identifiers

The field identifier is designed to be easy to capture and communicate in both digital and non-digital formats without mistakes. It looks like this:


The system generates identifiers using a subset of the ASCII character set, with some important characteristics:

  • IDs are always unique
  • Only capital letters, numbers and a period separator are used, eliminating case sensitivity issues
  • Letters that can be confused with numbers (I and O) are never included
  • The ID will always contain at least one letter, to ensure it cannot be confused for a decimal number
  • Use of vowels is controlled in such a way that the chance an ID can spell a word is limited
  • The word-only character set means a double-clicks selects the whole ID
  • A checksum is included to limit transcription errors

The validity of a field ID can always be checked by resolving it using the GET /fields/{id} API endpoint.

The period character is included for visual separation, its position is not important. In other words Field IDs with the period in the wrong place can’t mis-identify fields, and in fact Field IDs with and without it can be considered the same field.

Visual representation

Although it doesn’t affect the identity of the field per se, the period character should be included whenever displaying the ID, to provide visual separation that makes the ID easier to transcribe or read out over the telephone without mistakes.

The ID should always be labelled as a Global Field ID. When presented in limited space, the ID should be presented alongside the GFID tag to indicate it as such:

/\ 15KW.V5JZ

The tag comprises the character string /\ (slash and backslash, ASCII /\). It may optionally be colored (RGB 149,211,0, HTML #95D300). Care should be taken to visually separate the tag prefix from the ID itself to avoid inclusion of the tag within ID.


Some protocols use prefixed identifiers to distinguish identifiers of different schemes, for example the CURIE syntax, or IRI prefixes used in JSON-LD. In such cases We recommend using GFID as the prefix, i.e.: GFID:15KW.V5JZ

Boundary Identifiers

In the Global FieldID® system, boundaries are deduplicated spatial objects. Each boundary ID uniquely identifies a specific area on Earth: a common identifier for spatial features from any source with the same geometry. In other words, references to the same boundary ID always refer to the same geometry, and references to different boundary IDs are always referring to different areas of land, even if only slightly differing in the number of vertices, presence of holes etc - if the resulting spatial footprint of is different, it will be assigned a novel boundary ID.

Whenever a boundary is registered in the Global FieldID® system, it is always assigned the same boundary ID no matter which source it came from or any other metadata attached to it. This is accomplished by correcting and normalizing the boundary geometry and checking for matches with existing geometries.

Unlike a field, a boundary is considered to be a technical concept and therefore its identifier is intended for use in machine-to-machine communications. A Global Boundary ID is a UUID:


UUIDs are commonly used in data exchange protocols such as ISO 11783 and the ADAPT framework, as well as being well-supported in database engines for optimised index performance.

Note: A boundary ID is not intended for human display or recognition; different boundaries should be presented either spatially or using their associated metadata in order to distinguish them.

Boundary References

Part of the GFID service’s functionality is to deduplicate multiple instances of the same concepts from different systems, and give them a common (shared) Boundary identifier. However, each system typically has its own internal name or identifier for a field or boundary. Whilst we provide a Global Boundary ID that is common to all instances of the same geometry (see above), we also retain each individual ‘reference’ to the boundary, enabling client applications to translate between them.

When each system registers a boundary GeoJSON Feature (a feature comprising geometry and metadata), we retain it as a boundary reference. If the source includes its own identifier, we include it as a user_provided_key property, and clients can use it as a key to query the API. This allows a 3rd party identifier to be resolved to its canonical Global Boundary ID, and vice versa.

However, IDs provided by the source cannot be guaranteed to be unique across or even within sources (e.g. it is common to reuse the same ID for a feature with the same or similar geometry, but different metadata). Therefore a boundary reference is assigned a globally unique primary identifier, which is a UUID.

In summary:

  • The ID of a boundary is a Global Boundary ID (a UUID)
  • A boundary has one or more boundary references linked to it
  • The ID of boundary reference is a UUID
  • A boundary reference has a source, and may have a ‘user provided key’ (any string)