NLDI and Geoconnex

How the Network Linked Data Index (NLDI) relates to geoconnex.us, persistent identifiers, and hydrographic addressing.

Overview

The NLDI is a search engine that indexes data using the river network as its
organizational backbone. It supports discovery of hydrologically linked features
by indexing information to NHDPlus catchments and hydrographic network elements.

The geoconnex.us system complements the NLDI by providing persistent, public‑domain
identifiers for environmental features. These identifiers act similarly to DOIs and
can redirect clients to current authoritative locations for environmental information.

What is geoconnex.us?

Geoconnex.us is a public domain registry operated to provide persistent
identifiers for environmental features. It allows a stable URI such as:

https://geoconnex.us/usgs/monitoring-location/08279500

to redirect to a current authoritative page:

https://waterdata.usgs.gov/monitoring-location/08279500/

Because the redirect can change, geoconnex enables:

  • Long‑term stability of identifiers
  • Freedom for organizations to restructure URLs
  • Reliable linking across distributed systems

How NLDI and Geoconnex Interact

Hydrographic addressing (using reachcode and measure attributes) allows features
to be precisely located on the hydrographic network.
These addresses can be registered with geoconnex.us, and the same identifiers
can be indexed by the NLDI.

This creates a linkage between:

  • Hydrologic network indices (NLDI)
  • Persistent feature identifiers (geoconnex)
  • Authoritative data providers (e.g., waterdata.usgs.gov)

Together, the systems support robust environmental linked data on the internet.

Scope Distinctions

It is important to distinguish the roles of the two systems:

  • geoconnex.us is only a registry.
    It does not store or serve geospatial data.

  • The NLDI is only an index and data service.
    It does not persist data beyond hydrographic network components.

This separation of concerns enables:

  • Flexibility in how data providers manage their systems
  • Independent evolution of indexing vs. persistent identification
  • Interoperability across agencies and data platforms

Reference Gages

The blog post introduces the concept of reference gages. These serve as common,
shared identifiers for stream monitoring locations used by multiple organizations.

Key points:

  • Many organizations measure data at the same real‑world location.
  • Each tends to maintain its own identifiers and spatial metadata.
  • Reference gages unify these descriptions under a shared identifier.

Using reference gages, an organization can link its data to:

  • A common geoconnex identifier
  • Authoritative provider metadata (e.g., NWIS site IDs)
  • Hydrologic network positions exposed by the NLDI

This supports cross‑platform data integration and discovery.

Example of Reference Gage Workflow

The geoconnex identifier:

https://geoconnex.us/ref/gages/1055733

Provides:

  • Provider information (e.g., USGS)
  • The provider’s identifier (e.g., an NWIS site number)
  • A link back to the authoritative monitoring location page

In turn, the authoritative site may include an “about” link back to the reference
gage identifier, completing a mutual linkage between systems.

Notes & TODOs

  • TODO: Add diagrams illustrating the relationship between NLDI, geoconnex, and data providers.
  • TODO: Document how the Python implementation may expose geoconnex IDs via JSON-LD or link headers.
  • TODO: Provide best practices and patterns for linking NLDI-discovered features to geoconnex identifiers.