Working with ENC (S-57) data presents a very specific challenge: their richness and complexity make any “blind” approach inefficient. Even before discussing data import or structuring in QGIS, a fundamental question arises: which charts should be loaded, and why choose these rather than others?
This is precisely where the NOAA ENC catalogue comes into play — a resource that is still largely underused by GIS professionals.
After presenting how to import ENC S-57 data into QGIS with S57Manager — first using PostGIS, then GeoPackage — this final article focuses on a crucial but often overlooked step: exploring and selecting the relevant ENC cells upstream of the import process, using the official NOAA ENC catalogue.
ENC Data: Abundance That Complicates Choice
Unlike conventional GIS datasets, an ENC does not correspond to a single map covering a given area. Instead, it belongs to a set of chart cells, each defined by:
- a precise geographic extent,
- a nominal scale,
- a cartographic usage (overview, coastal, approach, harbour, berth…),
- a navigation purpose.
For the same geographic area, several ENC cells may overlap at different scales. Importing all available ENC data without prior selection quickly leads to:
- oversized databases,
- unreadable QGIS projects,
- degraded performance,
- and above all, a loss of cartographic meaning.
Before exploiting ENC data, it is therefore essential to understand and contextualize it.
The NOAA ENC Catalogue: A Key but Raw Resource
NOAA (National Oceanic and Atmospheric Administration) provides an official ENC catalogue, distributed as an XML file compliant with ISO standards (notably ISO 19115).
For each ENC cell, the catalogue contains:
- a unique identifier (cell_id),
- a name,
- a scale,
- a usage / purpose,
- a geographic extent,
- an official download URL.
In theory, all the information required for informed selection is available. In practice, however, this catalogue is difficult to exploit:
- XML format is hard to read,
- no direct spatial visualization,
- consultation often limited to specialized tools or ad hoc scripts.
The challenge is therefore clear: transform this technical catalogue into a usable GIS layer in QGIS.
From XML Catalogue to a Spatial Index Layer
Once the NOAA catalogue is properly parsed, it becomes possible to extract the geographic extents of all ENC cells and convert them into polygons.
The result is a spatial index layer, typically stored in a GeoPackage, containing:
- one polygon per ENC cell,
- essential attributes:
- cell_id
- name
- scale
- purpose
This layer is lightweight, stable, and only needs to be generated once. It does not contain any detailed nautical geometry — only chart extents.
Loading and Exploring NOAA Extents in QGIS
Once loaded into QGIS, this index layer becomes a highly effective exploration tool:
- transparent polygons to preserve background readability,
- visible outlines to distinguish cells,
- labels displaying the cell identifier,
- easy overlay with:
- a study area,
- an existing project,
- field data.
Within seconds, it becomes possible to:
- identify which ENC cells actually cover the area of interest,
- compare available scales,
- understand the charting logic,
- avoid unnecessary imports.
Here, QGIS fully regains its role as a spatial analysis tool, not just a data viewer.
From Exploration to Import: Integration with S57Manager
The true value of this index layer emerges when it is connected to S57Manager.
Directly from QGIS, the user can:
- visually explore ENC extents,
- select a relevant cell,
- trigger the import of that cell via a QGIS action.
This workflow enables:
- targeted imports,
- fine control over data volume,
- alignment between operational needs and loaded data,
- full compatibility with both storage modes supported by S57Manager:
- PostGIS,
- GeoPackage.
The workflow shifts from “import then sort” to “understand, select, then import.”
Conclusion: Bringing Intelligence Upstream
By exploiting the NOAA catalogue as a GIS layer, working with ENC data becomes clearer and more efficient. Instead of suffering from the complexity of S-57 data, GIS professionals regain control from the very first step: exploration, selection, and decision-making.
Combined with S57Manager, the NOAA catalogue is not an auxiliary tool, but the first building block of a coherent processing chain:
catalogue → selection → import → exploitation
A step too often overlooked — yet essential for working confidently with complex nautical data in QGIS.
