NativeGB — Dacorum regional basemap measurement
Measured 17 October 2026. All sizes use decimal MB (1 MB = 1,000,000 bytes).

Authority: Dacorum, Hertfordshire — ONS code E07000096.
Boundary: ONS Local Authority Districts, December 2025, BGC (20 m generalised,
coastline clipped). Original EPSG:27700 geometry was used for extraction.
Source: https://www.data.gov.uk/dataset/e2f256dc-9313-487b-8190-46b0da8c2798/local-authority-districts-december-2025-boundaries-uk-bgc

Regional bundle: 33,296,785 bytes = 33.296785 MB, rounded to 33.3 MB.
Mapping payload: 33,250,559 bytes.
- TrueScale: 23,218,964 bytes (18 whole 5 km tiles).
- Detailed overview: 309,551 bytes (18 tiles).
- Low/national overview: 9,375,374 bytes (18 scale-specific tile entries).
- Overview rasters: 346,670 bytes (9 files).
Manifests, boundary metadata and extraction report: 46,226 bytes.
ZIP container, without additional compression: 33,300,063 bytes.

Selection: whole vector tiles intersecting the actual polygon, no added buffer.
Rasters are cropped to the council boundary's bounding box. The package therefore
includes mapping beyond the council line. It is not polygon-clipped street data.
This is a measured local extraction, not a customer deployment or a demonstration
of importing the regional bundle into TerraForm. Gazetteer, records, photos,
application/browser storage and other datasets are excluded.

Verification: extractor checks passed for every pack/tile/raster. Independent
Shapely polygon intersection selected exactly the same tiles in all three vector
tiers. Each extracted vector tile's SHA-256 matched bytes read from the original
source pack. The ZIP passed a full integrity test; file sizes and SHA-256 values
are recorded in the accompanying local measurement JSON.

National comparison: the existing NativeGB vector packs measured 8,176,761,908
bytes (8.18 GB). Their measured filesystem sizes agree with their manifests.
That national figure is the vector corpus; the Dacorum bundle also includes its
regional rasters and metadata. This film makes no fixed percentage-saving claim.
Other authorities and source releases will have different package sizes.

Source: Office for National Statistics licensed under the Open Government Licence v.3.0
Contains OS data © Crown copyright and database right 2026.
Map shapes are from ONS data. The selection grid represents actual TrueScale tiles.
The GB outline is dissolved from the same ONS council dataset, with Northern
Ireland excluded. Display simplification does not change extraction geometry.