GeoDjango in a nutshell

GeoDjango in a nutshell
Vasyl Dizhak
http://djangostars.com/

Friday, August 26, 2011

• Into
• Standards
• Django/GeoDjango
• Demo app
• Open source


“80% of projects and
services include spatial
data” Cliché


“nere things are more
related than distant
things”
W.R.Tobler (1970)


Geographic information
systems(GIS)
• Standards, spatial
data, coordinate
systems

• Maps are ﬂat, world is
not


Coordinate systems
Geodetic (coordinates are in angels latitude/
longitude)
Projected (represents world surface in a ﬂat way,
using linear units and play with various distortions)


Standards
• OGC: Open Geospatial Consortium. Inc.

• Promulgates standards for geospatial
and location based services

• SFS: Simple Feature Access for SQL

• OGC standard for spatial databases

• The most popular

• WKT: Well Known Text

• Geometries

• Coordinate systems


• WKB: Well Known Binary

• Binary representation of geometries

• HEX: Binary

• EWKT

• EWKB, HEXEWKB

• GML: Geometry Markup Language (XML based)

• KML: Keyhole Markup Language

• Google Earth/Maps Format

• WMS: Web Mapping Service(serves up images)

• WFS: Web Feature Service (serves up vector data)


Near things
• GeoJSON: Geometry JSON (not in OGC
standard)

• SRS: Spatial Reference System

• CRS: Coordinate Reference System (same as SRS)

• EPSG: European Petroleum Survey Group

• SRID: Spatial Reference Indeniﬁer (corresponds to
EPSG number)


Geometry objects

• Point
• LineString
• LinearRing
• Polygon

• MultiPoint

• MultiString

• MultiPolygon

• GeometryCollection


Django

• Python based framework
• Powerful ORM
• MTV concepts
• Support unix and windows platforms


GeoDjango

• Based on the top of django, so include all
beneﬁts :)
• Include python interfaces for GEOS,
GDAL, GeoIP thanks to ctypes support in
python


http://houstoncrimemaps.com/


History
• Initially created by Justin Bronn
• Started in 2006
• 2008 - 1.0 release
• 2009 - 1.1 release
• 2010 - 1.2 release
• 2011 - 1.3 release

Real using

http://www.everyblock.com/


• http://www.nytimes.com/
• http://projects.latimes.com/mapping-la/
neiborhoods/

• http://marinemap.org/
• http://earth.burningman.com/
• http://about.nsw.gov.au/
• and others ...


GEOS
• Geometry Engine Open Source
In [3] from django.contrib.gis.geos import *

In [4]: point = GEOSGeometry('Point(0 10)')

In [5]: point.coords

Out[5]: (0.0, 10.0)


In [7]: coords = ((0, 0), (0, 10), (10, 13), (0, 0))

In [8]: polygon = Polygon(coords)

In [9]: mpolygon = MultiPolygon(polygon)


In [33]: polygon.wkt

Out[33]: 'POLYGON ((0.0000000000000000 0.0000000000000000,
0.0000000000000000 10.0000000000000000, 10.0000000000000000 13.0000000000000000,
0.0000000000000000 0.0000000000000000))'

In [34]: polygon.contains(Point(11, 12))

Out[34]: False

In [35]: polygon.json

Out[35]: '{ "type": "Polygon", "coordinates":
[ [ [ 0.000000, 0.000000 ], [ 0.000000, 10.000000 ],
[ 10.000000, 13.000000 ], [ 0.000000, 0.000000 ] ] ] }'

In [36]: polygon.kml

Out[36]: '<Polygon><outerBoundaryIs><LinearRing>
<coordinates>0.0,0.0,0 0.0,10.0,0 10.0,13.0,0 0.0,0.0,0</coordinates>
</LinearRing></outerBoundaryIs></Polygon>'


GDAL
Geospatial Data Abstraction Library
In [2]: from django.contrib.gis.gdal import *
...
In [28]: k = DataSource('data/ukraine_administrative.shp')
In [29]: layer = k[0]
In [30]: layer
Out[30]: <django.contrib.gis.gdal.layer.Layer object at
0x10325f990>
In [31]: len(layer)
Out[31]: 9976
In [32]: layer.ﬁelds
Out[32]: ['NAME', 'ADMIN_LEVE']

You can transform coordinates from one projection to
another

In [37]: s = SpatialReference(4326)

In [39]: k = GEOSGeometry('Point(10 10)', s)

In [40]: k.transform(900913)


GeoIP
IP-based Geolocation binding to MaxMind
In [1]: from django.contrib.gis.utils import GeoIP
In [2]: g = GeoIP()
In [6]: g.country('it-jam.ciklum.net')
Out[6]: {'country_name': 'Ukraine', 'country_code': 'UA'}
In [7]: g.city('it-jam.ciklum.net')
Out[7]: {'city': None, 'region': None, 'area_code': 0, 'longitude': 32.0, 'country_code3': 'UKR',
'latitude': 49.0, 'postal_code': None, 'dma_code': 0, 'country_code': 'UA', 'country_name':
'Ukraine'}
In [8]: g.geos('it-jam.ciklum.net')
Out[8]: <Point object at 0x103482fd0>
In [9]: g.geos('it-jam.ciklum.net').coords
Out[9]: (32.0, 49.0)


Geometry Fields
• GeometryField

• PointField

• LineStringField

• PolygonField

• MultiPointField

• MultiLineStringField

• MultiPolygonField

• GeometryCollectionField


Models example

from django.contrib.gis.db import models

class Checkin(models.Model):
type = models.CharField(max_length=1, choices=CHECKIN_TYPE)
title = models.CharField(max_length=255, blank=True, null=True)
geodata = models.PointField()
updated = models.DateTimeField(auto_now=True)

objects = models.GeoManager()


PostgreSQL SQL


Geometry Field Options
• srid (Spatial Reference System Identity,
corresponding to spatial_ref_sys db
table, default is 4326)
• spatial_index (Spatial indexes are created
by default)
• dim (Set dimension if backend supports
this, default is 2, postgis only)
• geography


Spatial Lookups


Lookup types
PostGIS is a rock star :)
As parameters lookups
can be any data that can
be converted into GEOS
geometry like
GeoJSON, WKT etc.

https://docs.djangoproject.com/en/dev/ref/contrib/gis/db-api/#spatial-lookup-compatibility


Example
In[8]: pnt = Point(40.187953, 49.9658546)

In[9]: Administrative.objects.get
(geodata__contains=pnt)

Out[10]: <Administrative: 9976>


Measurement objects

Conversation between measurement units


Distance, D
In [1]: from django.contrib.gis.measure import D

In [2]: dist = D(km=500)

In [3]: dist.mi

Out[3]: 310.68559611866698

In [4]: dist.rod

Out[4]: 99419.390757973422


Area, A
In [1]: from django.contrib.gis.measure import A

In [2]: a = A(sq_m = 10)

In [3]: a.sq_km

Out[3]: 1.0000000000000001e-05

In [4]: a.sq_rod

Out[4]: 0.39536861034746451


Distance queries*
In [10]: Checkin.objects.ﬁlter(geodata__distance_gte=(pnt, 7000))

Out[10]: [<Checkin: Ресторан «Домашня Кухня»>, <Checkin:
Великий Вiз>, <Checkin: Ресторан «Домашня Кухня»>,
<Checkin: Станція швидкісного трамвая "Польова">, <Checkin:
НТУУ "КПИ", корпус 7>]


GeoQuerySet Methods

MySQL does not
support any of these

more ...


Aggregate Methods

• collect
• extend
• extend3d
• make_line
• unionagg


Output methods
Done more on db level

• kml()
• gml()
• svg()
• geojson()
• geohash()


Measurement methods

• area()(attachs the area to each geometry
ﬁeld in the queryset as Area object )
• distance(geom)
• length()
• perimeter()


Geometry operations

• difference(geom)
• intersection(geom)
• union(geom)
• sym_difference(geom)


Geometry methods
• centroid()
• envelope()
• point_on_surface()
• scale(x, y, z=0)
• translate(x, y, z=0)
• transform(srid)

In [10]: k = Administrative.objects.kml().svg().perimeter
().point_on_surface().get(id=10)

In [11]: k.point_on_surface.coords

Out[11]: (22.153155999999999, 48.512821000000002)

In [12]: k.kml

Out[12]:
u'<LineString><coordinates>22.166018,48.5771299


Show time


Related projects

• FeatureServer http://featureserver.org
• TileCache http://tilecache.org
• TileStache http://tilestache.org/
• Mapproxy http://mapproxy.org/


Cartography

• Mapnik http://mapnik.org
• MapServer http://mapserver.org


Frontend interaction
• OpenLayers http://openlayer.org
• Google maps js api
• Polymaps http://polymaps.org/
• Wax http://mapbox.github.com/wax/
manual/
• TileMill http://tilemill.com/pages/index.html

Many thanks
Vasyl Dizhak
http://twitter.com/rootart
http://twitter.com/djangostars
http://geojam.djangostars.com
http://github.com/rootart/geojam
Questions?


GeoDjango in a nutshell

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