Drawing and Labelling Parallels and Meridians¶
  <#drawing-and-labelling-parallels-and-meridians>

Most maps include a graticule grid, a reference network of labelled
latitude and longitude lines. Basemap does this with the
|drawparallels()|
<https://matplotlib.org/basemap/api/basemap_api.html#mpl_toolkits.basemap.Basemap.drawparallels>
and |drawmeridians()|
<https://matplotlib.org/basemap/api/basemap_api.html#mpl_toolkits.basemap.Basemap.drawmeridians>
instance methods. The longitude and latitude lines can be labelled where
they intersect the map projection boundary. There are a few exceptions:
meridians and parallels cannot be labelled on maps with |proj| set to
|ortho| (orthographic), |geos| (geostationary), |vandg| (van der
Grinten) or |nsper| (near-sided perspective), and meridians cannot be
labelled on maps with |proj| set to |ortho| (orthographic), |geos|
(geostationary), |vandg| (van der Grinten), |nsper| (near-sided
perspective), |moll| (Mollweide), |hammer| (Hammer), or |sinu|
(sinusoidal). This is because the lines can be very close together where
they intersect the boundary on these maps, so that they really need to
be labelled manually on the interior of the plot. Here’s an example that
shows how to draw parallels and meridians and label them on different
sides of the plot.

from mpl_toolkits.basemap import Basemap
import matplotlib.pyplot as plt
import numpy as np
# setup Lambert Conformal basemap.
m = Basemap(width=12000000,height=9000000,projection='lcc',
            resolution='c',lat_1=45.,lat_2=55,lat_0=50,lon_0=-107.)
# draw coastlines.
m.drawcoastlines()
# draw a boundary around the map, fill the background.
# this background will end up being the ocean color, since
# the continents will be drawn on top.
m.drawmapboundary(fill_color='aqua')
# fill continents, set lake color same as ocean color.
m.fillcontinents(color='coral',lake_color='aqua')
# draw parallels and meridians.
# label parallels on right and top
# meridians on bottom and left
parallels = np.arange(0.,81,10.)
# labels = [left,right,top,bottom]
m.drawparallels(parallels,labels=[False,True,True,False])
meridians = np.arange(10.,351.,20.)
m.drawmeridians(meridians,labels=[True,False,False,True])
plt.show()

(Source code <https://matplotlib.org/basemap/users/figures/graticule.py>)

../_images/graticule.png


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      o Download <https://matplotlib.org/basemap/users/download.html>
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©2011, Jeffrey Whitaker; 2016 The matplotlib development team. | Powered
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