You're looking at a satellite image of the UK, with every Site of Special Scientific Interest (SSSI) plotted on top of it. Zoomed out like this (below zoom level 12), each site is shown as a small orange dot marking its centre.

Zoom in and, from level 12, that dot resolves into the site's actual boundary — a rough outline at first, becoming progressively more detailed until, from around zoom level 14, you see the full, precise shape of the site.

Hover over a site's outline to preview it, or click it to load its full description below the map. From there, click "View full site page" for the complete picture — description, species, habitats, condition, geology and more, all brought together in one place. Click the red target marker to list the ten closest interesting sites to that point — click any orange name in that list to jump straight to that site.