> For the complete documentation index, see [llms.txt](https://docs.os.uk/os-downloads/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.os.uk/os-downloads/products/areas-and-zones-portfolio/boundary-line/boundary-line-product-information/structure-of-boundary-line.md).
# Structure of Boundary-Line
Boundary-Line data is output in a layered structure. This is a simplified file structure whereby the boundaries are supplied as individual files; for example, the county file contains only counties.
An example of the GB directory and layered files.
An example of the Polling Districts England directory and layered files.
An example of the Wales directory and layered files.
{% hint style="info" %}
Ceremonial and Historical counties are provided in separate directories called Supplementary\_Ceremonial and Supplementary\_Historical, respectively. Historic European Regions are provided in a separate Supplementary\_Historic\_European\_Region directory and Country outlines are provided in a separate Supplementary\_Country directory.
{% endhint %}
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