Isoband.jl wraps isoband_jll, which gives access to wilkelab's isoband package, which powers contour plots in ggplot.
] add Isoband
xs = 0:10 # correspond to columns of zs
ys = 0:20 # correspond to rows of zs
zs = ys * xs'
# there are single band / line methods...
one_band = isobands(xs, ys, zs, 0, 10)
# access polygon data
one_band.x
one_band.y
one_band.id
one_line = isolines(xs, ys, zs, 5)
# ...and multi band / line methods
multiple_bands = isobands(xs, ys, zs, [0, 1, 10], [1, 10, 100])
multiple_lines = isolines(xs, ys, zs, [1, 10, 20])
# access first line data
multiple_lines[1].x
multiple_lines[1].y
multiple_lines[1].id