New: the Shapely Manual

Shapely

Shapely is a package for manipulation and analysis of 2D geospatial geometries.

It is based on GEOS (http://geos.refractions.net). Shapely 1.0 is ignorant about coordinate and reference systems. Projection responsibility is left to specific applications.

Shapely requires Python 2.4+. (I've also begun to port it to Python 3.0: http://zcologia.com/news/564/shapely-for-python-3-0/)

Capabilities

  • Obtain the unions, intersections, or differences of 2D shapes
  • Determine whether 2D shapes intersect, touch, or contain one another

and more

Dependencies

  • libgeos_c (2.2.3 or 3.0.0+)

Installation

Windows users should use the executable installer, which contains the required GEOS DLL. Other users should acquire and install libgeos_c by any means, such as by executing 

$ apt-get install libgeos-c1

Then install from the Python package index: 

$ easy_install Shapely

or with the setup script from svn: 

$ svn co http://svn.gispython.org/svn/gispy/Shapely/trunk Shapely
$ cd Shapely
$ python setup.py install

or by using the development buildout, which also provides libgeos_c (this does not seem to work with Python 2.5.x on Windows at least): 

$ svn co http://svn.gispython.org/svn/gispy/buildout/shapely.buildout/trunk shapely.buildout
$ cd shapely.buildout
$ python bootstrap.py
$ ./bin/buildout

Usage

Buffer a point: 

>>> from shapely.geometry import Point
>>> point = Point(-106.0, 40.0) # longitude, latitude
>>> point.buffer(10.0)
<shapely.geometry.polygon.Polygon object at ...>

See Operations.txt and Predicates.txt under tests/ for more examples of the spatial operations and predicates provided by Shapely. Also see Point.txt, LineString?.txt, etc for examples of the geometry APIs.

Numpy integration

All Shapely geometry instances provide the Numpy array interface: 

>>> from numpy import asarray
>>> a = asarray(point)
>>> a.size
3
>>> a.shape
(2,)

Numpy arrays can also be adapted to Shapely points and linestrings: 

>>> from shapely.geometry import asLineString
>>> a = array([[1.0, 2.0], [3.0, 4.0]])
>>> line = asLineString(a)
>>> line.wkt
'LINESTRING (1.0000000000000000 2.0000000000000000, 3.0000000000000000 4.0000000000000000)'

Python Geo Interface

Any object that provides the Python geo interface can be adapted to a Shapely geometry with the asShape factory: 

>>> d = {"type": "Point", "coordinates": (0.0, 0.0)}
>>> from shapely.geometry import asShape
>>> shape = asShape(d)
>>> shape.geom_type
'Point'
>>> tuple(shape.coords)
((0.0, 0.0),)

>>> class GeoThing(object):
...     def __init__(self, d):
...         self.__geo_interface__ = d
>>> thing = GeoThing({"type": "Point", "coordinates": (0.0, 0.0)})
>>> shape = asShape(thing)
>>> shape.geom_type
'Point'
>>> tuple(shape.coords)
((0.0, 0.0),)

See http://trac.gispython.org/projects/PCL/wiki/PythonGeoInterface for more details on the interface.

Testing

Several of the modules have docstring doctests: 

$ cd shapely
$ python point.py

There are also two test runners under tests/. test_doctests.py requires zope.testing. runalldoctests.py does not.

Known Issues

There are several upstream issues with GEOS versions 2.2.3 and 3.0.0. The GEOS WKT and WKB writers leak, and so therefore does access of a geometry's *wkt* and *wkb* properties. There are smaller leaks associated with creation of some geometry types.

Support

If you have questions, please consider joining our community list:

http://trac.gispython.org/projects/PCL/wiki/CommunityList