[Solved] “PROJ_LIB” error when installing Basemap on Windows using Anaconda

As an Anaconda user, I love how convenient it is to install packages. So when I tried install Basemap using conda as usual:

conda install -c anaconda basemap

And import it in Jupyter Notebook:

from mpl_toolkits.basemap import Basemap

I was shocked that I got an error message:

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-2-702dba317ad4> in <module>()
      1 
----> 2 from mpl_toolkits.basemap import Basemap

~\Anaconda3\lib\site-packages\mpl_toolkits\basemap\__init__.py in <module>()
    153 
    154 # create dictionary that maps epsg codes to Basemap kwargs.
--> 155 pyproj_datadir = os.environ['PROJ_LIB']
    156 epsgf = open(os.path.join(pyproj_datadir,'epsg'))
    157 epsg_dict={}

~\Anaconda3\lib\os.py in __getitem__(self, key)
    667         except KeyError:
    668             # raise KeyError with the original key value
--> 669             raise KeyError(key) from None
    670         return self.decodevalue(value)
    671 

KeyError: 'PROJ_LIB'

I googled for solution, and it seems to be a problem with conda not Basemap. Some people suggested installing using pip, but I still got error message when installing with pip.

And then I figured out that the path “PROJ_LIB” is needed for the file epsg. So where is the file? I looked at the Basemap documentation and it said:

The epsg codes supported by Basemap are at the file /mpl_toolkits/basemap/data/epsg.

Yet, I couldn’t even find the “data” folder under the basemap directory.

Luckily, I got a MacBook near me, which has Basemap installed (and it worked). So I looked at the “PROJ_LIB” variable, and copy the epsg file in the folder and paste to the basemap folder on my Windows computer.

Update: As mentioned in the comments, the epsg file can also be found on GitHub in the basemap repository! 

Before importing Basemap, I added this two lines.

import os
os.environ['PROJ_LIB'] = 'C:/Users/USERNAME/Anaconda3/Lib/site-packages/mpl_toolkits/basemap'

And it worked.

from mpl_toolkits.basemap import Basemap
 m = Basemap(projection='cyl', resolution='l', 
             llcrnrlat=-90, urcrnrlat = 90, 
             llcrnrlon=-180, urcrnrlon = 180)
 m.drawcoastlines(linewidth=0.5)

This is, of course, not the best solution of the problem, because you have to define the “PROJ_LIB” everytime you use Basemap. Still, I think it is quick enough if you don’t want to bother with pip.