Where would the static eval like each piece to be? For every piece in the position a worker lifts it and puts it on each empty square in turn, asking the engine for the eval each time. The heat maps show the change from the eval of the position as it stands, from the point of view of the piece's owner, red where the piece would be better placed and blue where it would be worse, on one colour scale shared by all the maps. Unlike the piece square tables this includes everything else in the eval, material interactions, king shelter and so on, in the context of this position. Castling rights and en passant are dropped first so the moved pieces do not leave stale rights behind. Hover a square for the number. Pieces are lifted without any regard to legality, so a king may sit in check.