Make contours better

[emeeks]

Contour data has a different styling format. You should be able to use the same style function for grid & hexbin for contour.

• Make the densest contour = 1 and others less dense

[emeeks]

1.16.1 now includes a percent prop for contours that indicates its percentage compared to the maximum value of a contour (contour value is point density per pixel so this is a very weird thing but ultimately maps up well to the percent-of-max seen in hexbin and heatmap)