How to plot selected contour lines?

Q&A GMT.jl Q&A
1

How do I add contour lines of a specific value, e.g., 1, to a filled contour? Thanks.

Below is my current code:

  # Defining the coast:
    coast(region=(20,380,-90,90));

    VAR_grid = mat2grid(Array(transpose(VAR)), x=Lon, y=Lat);
    grdimage!(VAR_grid, color=cpt1, nan_alpha=true, shade=false);

    # Plot the land map, clipping water leaving land:
    cpt0 = grd2cpt(Land_clip, color="250/240/230,250/240/230"); #:geo

    grdimage!(Land_clip, color=cpt0, nan_alpha=true, shade=false,
    xaxis=(annot=60, grid=30, FONT_ANNOT_PRIMARY="12p,Helvetica,black",),
    yaxis=(annot=30, grid=15, FONT_ANNOT_PRIMARY="12p,Helvetica,black",),
    par=(MAP_GRID_PEN_PRIMARY="0.005p",), coast=true);

    colorbar!(color=cpt2, frame=(xlabel="$(VarN)",),
    par=(FONT_ANNOT_PRIMARY="10p,Times-Roman,black", FONT_LABEL="12p,Times-Roman,black"), pos=(anchor=:BC, length=(12.5,0.4), offset=(-0.2,0.6)));