Abstract
A (not necessarily proper) vertex colouring of a graph has clustering c if every monochromatic component has at most c vertices. We prove that planar graphs with maximum degree
$\Delta$
are 3-colourable with clustering
$O(\Delta^2)$
. The previous best bound was
$O(\Delta^{37})$
. This result for planar graphs generalises to graphs that can be drawn on a surface of bounded Euler genus with a bounded number of crossings per edge. We then prove that graphs with maximum degree
$\Delta$
that exclude a fixed minor are 3-colourable with clustering
$O(\Delta^5)$
. The best previous bound for this result was exponential in
$\Delta$
.