Reading the chart
Your anchor sits at the centre with your swing circle around it; your boat lies to leeward and swings as the wind veers. The neighbour's circle turns red when it overlaps yours — that is the water you could both occupy. Keep the circles apart, allow for wind shifts, and remember the figures assume everyone swings the same way. For the full picture, see the swing circle guide and what radius should you set?
Frequently asked questions
The swing circle radius is roughly the horizontal distance from the anchor to the bow plus your boat length. That horizontal distance is close to the length of rode you let out, so as a quick guide the radius is about your rode length plus your boat length, centred on the anchor.
Far enough that their swing circles do not overlap. That means the distance between two anchors should be at least the sum of the two boats' swing radii, with a margin for wind shifts and boats that swing differently on chain versus rope.
Because their swing circles overlap, or because they swing differently. A boat on all chain sits closer to its anchor and swings tighter than one on rope, so two boats that look clear at slack water can meet when the wind fills in and they swing at different rates.