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72 changes: 50 additions & 22 deletions README.md
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Expand Up @@ -24,7 +24,7 @@ Pyshp is compatible with Python 2.4-3.x.

This document provides examples for using pyshp to read and write shapefiles.

Currently the sample census blockgroup shapefile referenced in the examples is available on the google code project site at
Currently the sample census blockgroup shapefile referenced in the examples is available on the GitHub project site at
[https://github.com/GeospatialPython/pyshp](https://github.com/GeospatialPython/pyshp). These
examples are straight-forward and you can also easily run them against your
own shapefiles manually with minimal modification. Other examples for specific
Expand All @@ -46,8 +46,8 @@ Before doing anything you must import the library.
>>> import shapefile

The examples below will use a shapefile created from the U.S. Census Bureau
Blockgroups data set near San Francisco, CA and available in the subversion
repository of the pyshp google code site.
Blockgroups data set near San Francisco, CA and available in the git
repository of the pyshp GitHub site.

## Reading Shapefiles

Expand Down Expand Up @@ -128,13 +128,17 @@ Each shape record contains the following attributes:
'points'
'shapeType'

* shapeType: an integer representing the type of shape as defined by the shapefile specification.
* shapeType: an integer representing the type of shape as defined by the
shapefile specification.


>>> shapes[3].shapeType
5

* bbox: If the shape type contains multiple points this tuple describes the lower left (x,y) coordinate and upper right corner coordinate creating a complete box around the points. If the shapeType is a Null (shapeType == 0) then an AttributeError is raised.
* bbox: If the shape type contains multiple points this tuple describes the
lower left (x,y) coordinate and upper right corner coordinate creating a
complete box around the points. If the shapeType is a
Null (shapeType == 0) then an AttributeError is raised.


>>> # Get the bounding box of the 4th shape.
Expand All @@ -143,12 +147,16 @@ Each shape record contains the following attributes:
>>> ['%.3f' % coord for coord in bbox]
['-122.486', '37.787', '-122.446', '37.811']

* parts: Parts simply group collections of points into shapes. If the shape record has multiple parts this attribute contains the index of the first point of each part. If there is only one part then a list containing 0 is returned.
* parts: Parts simply group collections of points into shapes. If the shape
record has multiple parts this attribute contains the index of the first
point of each part. If there is only one part then a list containing 0 is
returned.

>>> shapes[3].parts
[0]

* points: The points attribute contains a list of tuples containing an (x,y) coordinate for each point in the shape.
* points: The points attribute contains a list of tuples containing an
(x,y) coordinate for each point in the shape.

>>> len(shapes[3].points)
173
Expand Down Expand Up @@ -183,8 +191,12 @@ You can call the "fields" attribute of the shapefile as a Python list. Each
field is a Python list with the following information:

* Field name: the name describing the data at this column index.
* Field type: the type of data at this column index. Types can be: Character, Numbers, Longs, Dates, or Memo. The "Memo" type has no meaning within a GIS and is part of the xbase spec instead.
* Field length: the length of the data found at this column index. Older GIS software may truncate this length to 8 or 11 characters for "Character" fields.
* Field type: the type of data at this column index. Types can be: Character,
Numbers, Longs, Dates, or Memo. The "Memo" type has no meaning within a
GIS and is part of the xbase spec instead.
* Field length: the length of the data found at this column index. Older GIS
software may truncate this length to 8 or 11 characters for "Character"
fields.
* Decimal length: the number of decimal places found in "Number" fields.

To see the fields for the Reader object above (sf) call the "fields"
Expand Down Expand Up @@ -264,7 +276,7 @@ list of field values as demonstrated in the "Reading Records" section.
Let's read the blockgroup key and the population for the 4th blockgroup:


>>> shapeRecs3.record[1:3]
>>> shapeRecs[3].record[1:3]
['060750601001', 4715]

Now let's read the first two points for that same record:
Expand Down Expand Up @@ -295,17 +307,18 @@ The blockgroup key and population count:
There is also an iterShapeRecords() method to iterate through large files:

>>> shapeRecs = sf.iterShapeRecords()
>>> for shape, rec in shapeRecs:
>>> for shapeRec in shapeRecs:
... # do something here
... pass


## Writing Shapefiles

The PSL tries to be as flexible as possible when writing shapefiles while
PyShp tries to be as flexible as possible when writing shapefiles while
maintaining some degree of automatic validation to make sure you don't
accidentally write an invalid file.

The PSL can write just one of the component files such as the shp or dbf file
PyShp can write just one of the component files such as the shp or dbf file
without writing the others. So in addition to being a complete shapefile
library, it can also be used as a basic dbf (xbase) library. Dbf files are a
common database format which are often useful as a standalone simple database
Expand Down Expand Up @@ -333,9 +346,10 @@ shapefile specification. It is important to note that numbering system has
several reserved numbers which have not been used yet therefore the numbers of
the existing shape types are not sequential.

There are three ways to set the shape type: - Set it when creating the class
instance. - Set it by assigning a value to an existing class instance. - Set
it automatically to the type of the first shape by saving the shapefile.
There are three ways to set the shape type:
* Set it when creating the class instance.
* Set it by assigning a value to an existing class instance.
* Set it automatically to the type of the first shape by saving the shapefile.

To manually set the shape type for a Writer object when creating the Writer:

Expand Down Expand Up @@ -443,7 +457,8 @@ Creating attributes involves two steps. Step 1 is to create fields to contain
attribute values and step 2 is to populate the fields with values for each
shape record.

The following attempts to create a complete shapefile. The attribute and field names are not very creative:
The following attempts to create a complete shapefile. The attribute and
field names are not very creative:


>>> w = shapefile.Writer(shapefile.POINT)
Expand Down Expand Up @@ -523,7 +538,10 @@ write them.
## Editing Shapefiles

The Editor class attempts to make changing existing shapefiles easier by
handling the reading and writing details behind the scenes. This class is experimental and should be avoided for production use. You can do the same thing by reading a shapefile into memory, making changes to the python objects, and write out a new shapefile with the same or different name.
handling the reading and writing details behind the scenes. This class is
experimental and should be avoided for production use. You can do the same
thing by reading a shapefile into memory, making changes to the python objects,
and write out a new shapefile with the same or different name.

Let's add shapes to existing shapefiles:

Expand Down Expand Up @@ -566,17 +584,27 @@ Remove the last shape in the polygon shapefile.
>>> e.delete(-1)
>>> e.save('shapefiles/test/polygon')

## Python __geo_interface__
## Python \_\_geo_interface\_\_

The Python __geo_interface__ convention provides a data interchange interface
The Python \_\_geo_interface\_\_ convention provides a data interchange interface
among geospatial Python libraries. The interface returns data as GeoJSON. More
information on the __geo_interface__ protocol can be found at: [https://gist.g
information on the \_\_geo_interface\_\_ protocol can be found at: [https://gist.g
ithub.com/sgillies/2217756](https://gist.github.com/sgillies/2217756). More
information on GeoJSON is available at
[http://geojson.org](http://geojson.org)
[http://geojson.org](http://geojson.org).


>>> s = sf.shape(0)
>>> s.__geo_interface__["type"]
'MultiPolygon'

# Testing

The testing framework is doctest, which are located in this file README.md.
In the same folder as README.md and shapefile.py, from the command line run
```
$ python shapefile.py
```

Linux/Mac and similar platforms will need to run `$ dos2unix README.md` in order
correct line endings in README.md.
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