Differences between revisions 1 and 21 (spanning 20 versions)

Visualising spatial data

High level programming languages like e.g. Python, Matlab, R, IDL allow for the easy generation of maps by using specific modules. Alternatives to produce maps is special commerical or non-commercial software like e.g. ArcGIS, Generic mapping tool (GMT), ...

Map and projection basics

The Earth shape and it's approximation

How to do it in Python

There are different ways to generate maps with geographic information within Python. These are either based on the PyNGL (Gallery) or Basemap packages. PyNGL is very flexible to handle and allows for the generation of high quality maps. However, it takes a while to generate a nice looking map in PyNGL. If you just want to visualise your data, Basemap might be a very good alternative in many cases.

The Basemap way

Step 1: The first step is the generation of an Basemap object which includes also the definition of the projection. Which projection to choose depends on your application. You might want to have a map with specific properties like e.g. equal area or equal angular and optimized for a specific region like e.g. the polar regions.

   1 from mpl_toolkits.basemap import Basemap
   2 import matplotlib.pyplot as plt
   3 import numpy as np
   4 
   5 #/// define a map projection ///
   6 map = Basemap(projection='ortho', lat_0 = 50, lon_0 = -100,
   7               resolution = 'l', area_thresh = 1000.)
   8 
   9 #to see a list of potential projections, type help(Basemap)
  10 #be aware that each projection has different types of parameters
  11 
  12 #... you like coastlines?
  13 map.drawcoastlines()
  14 
  15 #... and countries
  16 map.drawcountries()
  17 
  18 #... fill continents
  19 map.fillcontinents(color = 'coral')
  20 
  21 #... draw coordinates
  22 map.drawmeridians(np.arange(0, 360, 30))
  23 map.drawparallels(np.arange(-90, 90, 30))

Load some vector data

References:

Cookbook / Matplotlib / Maps
Matplotlib Basemap Toolkit documentation
Snyder: Map projections - a reference manual

-  ⇤ ← Revision 1 as of 2011-02-09 19:19:11 → 
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+   ← Revision 21 as of 2011-02-10 19:43:53 → ⇥
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-Deletions are marked like this.
+Additions are marked like this.
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-#acl AdminGroup:read,write,delete,revert  EditorGroup:read,write StudentGroup:read,write
+#acl AdminGroup:read,write,delete,revert  EditorGroup:read,write StudentGroup:read
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+{{http://www.scipy.org/Cookbook/Matplotlib/Maps?action=AttachFile&do=get&target=basemap3c.png||height="399px",width="532px"}}
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+== Map and projection basics ==

[[EarthShape | The Earth shape and it's approximation ]]
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+There are different ways to generate maps with geographic information within Python. These are either based on the [[http://www.pyngl.ucar.edu/|PyNGL]] ([[http://www.pyngl.ucar.edu/Examples/gallery.shtml|Gallery]]) or [[http://matplotlib.sourceforge.net/basemap/doc/html/|Basemap]] packages. PyNGL is very flexible to handle and allows for the generation of high quality maps. However, it takes a while to generate a nice looking map in PyNGL. If you just want to visualise your data, Basemap might be a very good alternative in many cases.
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+Line 19:
-'''References:'''
 * [[http://www.scipy.org/Cookbook/Matplotlib/Maps | Cookbook / Matplotlib / Maps]]
 * [[http://matplotlib.sourceforge.net/basemap/doc/html/ | Matplotlib Basemap Toolkit documentation]]
+=== The Basemap way ===
 * '''Step 1:''' The first step is the generation of an Basemap object which includes also the definition of the projection. Which projection to choose depends on your application. You might want to have a map with specific properties like e.g. equal area or equal angular and optimized for a specific region like e.g. the polar regions.

{{{#!python
from mpl_toolkits.basemap import Basemap
import matplotlib.pyplot as plt
import numpy as np

#/// define a map projection ///
map = Basemap(projection='ortho', lat_0 = 50, lon_0 = -100,
              resolution = 'l', area_thresh = 1000.)

#to see a list of potential projections, type help(Basemap)
#be aware that each projection has different types of parameters

#... you like coastlines?
map.drawcoastlines()

#... and countries
map.drawcountries()

#... fill continents
map.fillcontinents(color = 'coral')

#... draw coordinates
map.drawmeridians(np.arange(0, 360, 30))
map.drawparallels(np.arange(-90, 90, 30))

}}}
-Line 20:
+Line 53:
+=== Load some vector data ===
'''References:'''

 * [[http://www.scipy.org/Cookbook/Matplotlib/Maps|Cookbook / Matplotlib / Maps]]
 * [[http://matplotlib.sourceforge.net/basemap/doc/html/|Matplotlib Basemap Toolkit documentation]]
 * Snyder: Map projections -  a reference manual