What's the difference between the BTO Atlas and the Wiltshire Tetrad Atlas?

The Wiltshire Tetrad Atlas aims to cover all tetrads in the county of Wiltshire. For the purposes of the Atlas a tetrad is considered to be in Wiltshire if at least 20% of its area lies within the county boundary.

Why do a Wiltshire Tetrad Atlas at the same time as the BTO Atlas?

Because the BTO supports the parallel production of local atlases (more than 30 are being done throughout the UK).

How is data collected for the Wiltshire Tetrad Atlas?

Invisibly - that is to say that, as far as the atlas volunteer is concerned, the data is submitted to the BTO via the existing online and offline channels provided for the BTO atlas. The BTO will identify the data within the area of Wiltshire and make it available to the Wiltshire Ornithological Society (WOS).