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GDAL must be installed:

Mac: NOTE: Add other flags, e.g. --with-postgresql, as desired

brew install gdal --complete --enable-unsupported --with-libkml

Ubuntu:

sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 16126D3A3E5C1192
sudo apt-get install python-software-properties -y
sudo add-apt-repository ppa:ubuntugis/ppa -y
sudo apt-get update -qq
sudo apt-get install libgdal-dev

ffi-ogr ... for convenient access to OGR functionality from Ruby

To run: bin/ogr_console

To read from a known file type (currently SHP, JSON/GeoJSON, CSV, raw Github GeoJSON URL, raw (spatial) CSV URL, Esri Feature Service URL):

data = OGR.read('https://raw.github.com/colemanm/hurricanes/master/fl_2004_hurricanes.geojson')
=> #<OGR::DataSource:0x007fb830aa3af8 @ptr=#<FFI::AutoPointer address=0x007fb8311ab990>>

# output to SHP file
data.to_shp '~/Desktop/github_to_shp.shp'
=> nil

# output to CSV file
data.to_csv '~/Desktop/github_to_csv.csv'
=> nil

To read from a PostGIS table:

pg_options = {
  'dbname' => 'my_db',
  'host' => 'localhost',
  'port' => 5432,
  'user' => 'user',
  'password' => 'p@$$w0rd'
}
# => {"dbname"=>"my_db", "host"=>"localhost", "port"=>5432, "user"=>"user", "password"=>"p@$$w0rd"}

# pg_options may also be a string path to a YAML file
pg_reader = OGR::PostgisReader.new pg_options
# => #<OGR::PostgisReader:0x007fce88943b90 @db_config="PG:dbname='my_db' host='localhost' port='5432' user='user' password='p@$$w0rd'", @driver=#<FFI::Pointer address=0x007fce8a22d8f0>, @type="PostgreSQL">

query = "select * from table_name where id = '49649d69-25a5-4dde-926d-b43a88c47d17'"
# => "select * from table_name where id = '49649d69-25a5-4dde-926d-b43a88c47d17'"

# output type of executed query is Layer
layer = pg_reader.execute_query query
# => #<OGR::Layer:0x007fce88b08390 @ptr=#<FFI::AutoPointer address=0x007fce8a20e0d0>>

layer.features
# => [#<OGR::Feature:0x007fce88af8008 @ptr=#<FFI::AutoPointer address=0x007fce8a2653b0>>, #<OGR::Feature:0x007fce88af3eb8 @ptr=#<FFI::AutoPointer address=0x007fce884e27b0>>]

To read a shapefile:

shp = OGR.read './spec/data/ne_110m_coastline/ne_110m_coastline.shp'
# => #<OGR::DataSource:0x007fba4d19c328 @ptr=#<FFI::AutoPointer address=0x007fba4c4cdc50>>

shp.to_geojson '~/Desktop/output.geojson'
# => Output GeoJSON to specified file

To reproject a shapefile:

shp = OGR.read './spec/data/ne_110m_coastline/ne_110m_coastline.shp'
# => #<OGR::DataSource:0x007fba4d19c328 @ptr=#<FFI::AutoPointer address=0x007fba4c4cdc50>>

shp.to_json
# => Output GeoJSON string

shp.to_json true
# => Output GeoJSON string (pretty print)

# epsg => import_sr(integer) or import_sr(integer, 'epsg'), proj4 => import_sr(string, 'proj4'), wkt => import_sr(string, 'wkt'), esri => import_sr(string, 'esri')
new_sr = OGR.import_sr 3857
# => #<OGR::SpatialReference:0x007fd859a0e6f8 @ptr=#<FFI::AutoPointer address=0x007fd85a11c100>>

shp.to_shp '~/Desktop/reprojected_shp.shp', {spatial_ref: new_sr}
# => Output reprojected SHP to specified file

To create a shapefile:

writer = OGR.create_writer '~/Documents/shapefiles/my_new.shp'

shp = writer.ptr

# add layer to shp : add_layer(name, geometry_type, spatial_reference)
# currently does not handle spatial reference, will automatically be nil
layer = shp.add_layer 'first_layer', :point

# add field to layer : add_field(name, field_type, options) NOTE: options are width and precision, defaulting to 32 and 1 respectively.
layer.add_field 'name', :string, width: 255

# create feature on layer
feature = layer.create_feature

# add field value to feature : set_field_value(field_name, field_value, field_type) NOTE: type can be inferred
feature.set_field_value 'name', 'my_feature'

# create point
point = OGR::Point.create [-104.789322, 38.992961]

# add point to first_feature
feature.add_geometry point

# add feature to first_layer
layer.add_feature feature

# sync to disk
layer.sync

A writer may be fetched by driver type:

writer = OGR.get_writer 'shp'
writer.set_output '~/Documents/shapefiles/my_new.shp'

Tested on: MRI (1.9/2.0), JRuby (1.9/2.0), and Rubinius (1.9/2.0)