# Basemap: adding a polygon covers up scatter plot on map

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.

Thanks,

Tim

from mpl_toolkits.basemap import Basemap

import numpy as np

from matplotlib.pyplot import *

from matplotlib.patches import Polygon

# 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()

# ---------------------

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., \

)
``````

# ---------------------

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()

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

···

On 2012/12/11 12:16 PM, Timothy Duly wrote:

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., \
)

# ---------------------
# 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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Thanks Eric, this did the trick. I did not know such a thing existed. Why “4”?

Tim

···

On Tue, Dec 11, 2012 at 4:35 PM, Eric Firing <efiring@…202…> wrote:

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

# 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()

# ---------------------

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., \
``````
``````     )
``````

# ---------------------

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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Thanks Eric, this did the trick. I did not know such a thing existed.
Why "4"?

I don't remember exactly what the defaults are for different types of artist, and didn't want to take the time to look, but I think they are all less than 4. So I just picked that as a value that would do the job.

Eric

···

On 2012/12/11 1:24 PM, Timothy Duly wrote:

Tim

On Tue, Dec 11, 2012 at 4:35 PM, Eric Firing <efiring@…202… > <mailto:efiring@…202…>> wrote:

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., \
> )
>
>
> # ---------------------
> # 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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services
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> _______________________________________________
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