Re: [Matplotlib-users] Basemap: adding a polygon covers up scatter plot on map

[Eric F. <ef...@ha...>]

On 2012/12/11 12:16 PM, Timothy Duly wrote:
> Hi,
>
> I'm running into a problem with overlaying a scatter plot on a polygon
> that is on a Basemap.  The polygon covers up the scatter plot created by
> the basemap.  To show the issue, the simple example below and broken
> down into three steps: 1) creating the map, 2) adding the red polygon,
> and 3) adding the "x" markers via a scatter plot.  You will see that the
> "x" markers are not on top of the polygon.
>
> Why does the polygon cover up the markers, even though I have the
> markers added after the polygon?  Would there be a better way to do
> this?  I could set the polygon alpha to, say, 0.5, but this feature does
> not show when I save it as an eps image.  Therefore, I would like to
> keep alpha=1.

Artists have a zorder attribute that controls the drawing order.  Try 
adding the kwarg zorder=4 to your scatter call.  I think that will take 
care of it.  (Alternatively you could lower the zorder of the polygon.)

Eric

>
> Thanks,
> Tim
>
> from mpl_toolkits.basemap import Basemap
> import numpy as np
> from matplotlib.pyplot import *
> from matplotlib.patches import Polygon
>
>
> # ---------------------
> # Part 1: Draw the map
> # ---------------------
>
> # Hawaii:
> lat_0 = 20.71-8.
> lon_0 = 203.83
>
> figure(1); clf();
> m = Basemap(width=2500e3,height=2500e3,
>          resolution='l',projection='stere', \
>                  lat_ts=lat_0,lat_0=lat_0,lon_0=lon_0)
>
> m.drawcoastlines()
> m.fillcontinents(color='coral',lake_color='aqua')
>
> # draw parallels and meridians:
> m.drawmapboundary(fill_color='aqua')
>
> lats = np.arange(np.floor(m.latmin),np.ceil(m.latmax),2.)
> lons = np.arange(190.,211.,5.)
> m.drawparallels(lats,labels=[True,False,False,False])
> m.drawmeridians(lons,labels=[False,False,False,True])
>
> draw(); show()
>
> # ---------------------
> # Part 2: Add a polygon
> # ---------------------
>
> lon_poly = np.array([-160., -150., -150., -160.,])
> lat_poly = np.array([10., 10., 14., 14.,])
> X, Y  = m(lon_poly, lat_poly)
> xy = np.vstack([X,Y]).T
>
> poly = Polygon(xy, closed=True, \
>          facecolor='red', \
>          linewidth=1., \
>          )
>
> gca().add_patch(poly)
>
> # ---------------------
> # Part 3: add some 'x' markers
> # ---------------------
>
> lon_markers = np.arange(-168.,-144.,2.)
> lat_markers = np.arange(5.,20.,1.)
> X, Y = np.meshgrid(lon_markers, lat_markers)
>
> x, y = m(X.ravel(), Y.ravel())
> m.scatter(x,y,marker='x')
>
> draw(); show()
>
>
>
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