CraggyIsland

This repository provides a catalogue of geospatial data files representing Irish administrative region boundaries which have been "simplified" to reduce file size.

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Problem 😣

Ireland is a craggy island. To plot its rugged coastline and historic regional boundaries in detail, modern geospatial data files require a huge amount of polygon coordinates. Generating interactive/responsive maps with so many coordinates can be an onerous task. Interactive plotting tools, such as Leaflet or Mapbox, can struggle to process and update highly-detailed maps in real time when used in applications like Shiny.

Solution 💡

To overcome this issue and improve the rendering process, the CraggyIsland repository provides a series of simplified administrative maps of Ireland. These simplified maps reduce polygon complexity by removing coordinates, while retaining topographical alignment (contiguous boundaries). The simplification process retains the general topographical profile of the original polygons (shape, centroid location, relative position), so viewers can still easily identify regions at a macroscopic level.

Furthermore, these files are stored in geoparquet format, heavily reducing the file size compared to geojson or geopackage alternatives.

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The Data

The original data files were sourced from Táilte Éireann's open data portal - GeoHive.
The region names, areas and (multi)polygons are present in every data file.
Administrative boundaries in the full data files of this repository are correct as of 2026.

The data files include the following administrative classifications:

• Nomenclature of Territorial Units for Statistics - 2 (NUTS2)
• Nomenclature of Territorial Units for Statistics - 3 (NUTS3)
• Provinces
• Counties
• Councils
• Municipal Districts (MDs)
• Local Electoral Areas (LEAs)
• Electoral Divisions (EDs)

For each administrative classification, data filename suffices correspond to the following level of polygon simplification:

• Full
  No simplification applied. Data is the same as the original source files.

• Simplified_1
  Approximately 5% of polygon coordinates are retained. Almost every polygon remains in place. Several of the smallest island polygons are discarded.

• Simplified_2
  Approximately 1% of polygon coordinates are retained. All major (inhabited) islands remain in place. Many minor (non-inhabited islands) are removed by over-simplification.

• Simplified_3
  Approximately 0.1% of polygon coordinates are retained. Most major inhabited islands remain, but some are removed by over-simplification including: Tory, Cape Clear, Valentia, Inisturk, Inishbofin (Donegal), Inisheer and Sherkin Islands. All non-inhabited islands are removed by over-simplification.
  This level of simplification converts regional boundaries into general outlines - not intended for mapping localities in detail.

• Simplified_Mainland_1
  Only polygons on the Irish mainland are kept. Approximately 5% of polygon coordinates are retained. Every regional (multi)polygon is kept.

• Simplified_Mainland_2
  Only polygons on the Irish mainland are kept. Approximately 1% of polygon coordinates are retained. Every regional (multi)polygon is kept.

• Simplified_Mainland_3
  Only polygons on the Irish mainland are kept. Approximately 0.1% of polygon coordinates are retained. Every regional (multi)polygon is kept.
  This level of simplification converts regional boundaries into general outlines - not intended for mapping localities in detail. Electoral division (ED) maps cannot be rendered at this level.

⚠️ NOTE: The simplification process will always retain a (multi)polygon for every administrative region, with the exception of EDs_Simplified_Mainland_2 where several island groups embodying whole EDs are not retained. These include Valentia, Inishmore, Aran, Inishbofin, Bear, Clare Island, Gorumna.

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Comparison of each administrative classification and simplification level.

Total number of polygon coordinates

Admin Class	Full	Simplified 1	Simplified 2	Simplified 3	Simplified Mainland 1	Simplified Mainland 2	Simplified Mainland 3
Provinces	2030872	114704	24600	2800	87249	18666	2124
NUTS2	2042880	115608	24851	2852	88402	18936	2178
NUTS3	832696	44244	10055	2044	31999	6892	1037
Counties	1317516	81077	23301	6109	67346	20278	5629
Councils	1466551	94533	28044	6628	80759	24966	6093
LEAs	7180672	412290	102787		396121	98890
MDs	2306810	133389	29124	3628	119458	25759	3248
EDs	2539978	147266	32351	4342	132830	28859	3945

Visual Comparison