This document introduces PostGIS, an extension to PostgreSQL that adds support for geographic objects allowing location queries to be run in SQL. It discusses geospatial data types and functions in PostGIS for working with spatial features like points, lines, polygons, and rasters. PostGIS allows importing and exporting geospatial data, integration with GIS software, and access to open mapping data sources. It also covers spatial queries and analysis in PostGIS using functions for distance, containment, intersections and more. Additional topics mentioned include pgRouting for routing/navigation, generating maps/images from PostGIS data, and real-world use cases.

1. Introducing PostGIS

2. What is Geospatial
• Most common use
– Narrow a search within a distance from a point of
origin
– Sort by that distance

3. Distance Formulas
• Flat-surface formulae
– Spherical Earth projected to a plane
– Ellipsoidal Earth projected to a plane
– Polar coordinate flat-Earth formula
• Spherical-surface formulae
– Haversine
– Tunnel distance
• Ellipsoidal-surface formulae
– Lambert’s formula for long lines
– Bowring’s method for short lines

4. Here’s one example

5. What you usually care about
• Given 2 latitude and longitude points
– Calculate the distance so we can find what’s close
• This is the common capability of databases with
“geospatial” support

6. A few options…
• Do the math in a query
• Here’s what it looks like in SQL
– (ACOS(least(1,COS(0.607198022186895)*COS(-
1.4410239410591847)*COS(RADIANS(latitude))*COS(RAD
IANS(longitude)) + COS(0.607198022186895)*SIN(-
1.4410239410591847)*COS(RADIANS(latitude))*SIN(RAD
IANS(longitude)) +
SIN(0.607198022186895)*SIN(RADIANS(latitude))))*39
63.19)) <= 25)
– Calculating within 25 miles of a point of origin based on an origin point
– You can do that in any database (it’s just math)
– Very intense query that slows as your dataset grows
– This…is not using an index

7. Speed that up
• Distance query a subset instead
• Use the lat/lng to create query a box
around the boundary
• Queried with a numerical index
• Then check the distance from center
for the subset
• NOTE: Doing this as part of another
query is a lot easier with multi-index
queries

8. And here’s what THAT looks like
WHERE (
latitude > 34.42845936786603
AND latitude < 35.15130863213399
AND longitude > -83.00467808012291
AND longitude < -82.12450191987708
)
AND
( (ACOS(least(1,COS(0.607198022186895)*COS(-
1.4410239410591847)*COS(RADIANS(latitude))*COS(RADIANS(longitude))+
COS(0.607198022186895)*SIN(-
1.4410239410591847)*COS(RADIANS(latitude))*SIN(RADIANS(longitude))+
SIN(0.607198022186895)*SIN(RADIANS(latitude))))*3963.19)
) <= 25)
Simple, am I right?
Also, you need to drop that distance formula into the ORDER BY clause too.

9. There’s a Gem for that!
Geokit
https://github.com/geokit/geokit
• Distance calculations between 2 points
– Multiple formulas and units of measure
• Multiple providers for Geocoding
different data
– Addresses
• Yahoo
• Geocoder.us/.ca
• Geonames
• Bing
• Yandex
• MapQuest
• Geocode.io
• Mapbox
• Google
• FCC
• Open Street Map
– IP Address
• hostip.info
• Geoplugin.net
• RIPE
• MaxMind (HIGHLY RECOMMEND)
• freegeoip.net
Geokit Rails (any database)
https://github.com/geokit/geokit-rails
• Premium Rails Integration
• ActiveRecord distance finders
• IP based location lookup
• Cookie based user location tracking
• Scopes: within, beyond, in_range, in_bounds,
closest, farthest, by_distance
• Generate the SQL
• Auto-Geocoding
• Mixin
class Location < ActiveRecord::Base
acts_as_mappable :default_units => :miles,
:default_formula => :sphere,
:distance_field_name => :distance,
:lat_column_name => :lat,
:lng_column_name => :lng
end

10. Actually, there’s several…
RGeo
• Adapters for
– MySQL
– SQLite
– PostGIS
• Process GeoJSON
• Read shapefiles
• Uses C++ extensions for
processing
Geocoder
• Object Geocoding
– IP
– Address
• Reverse Geocoding
– Address from lat/lng or IP
• Center of Multiple Locations
• Geographic Queries
– Near / nearby
– Distance
– Direction
• Easier to use
• Seems to be some dispute about
accuracy of data

11. What about PostgreSQL?
• Provide database functions
to handle this calculations
– Distance in straight line or
great circle
– Convert lat/lng to point
– Get lat/lng from a point
– Calculate containment
within a cube
• Point datatype
– Operator to get distance
between
Earth Distance extension
http://www.postgresql.org/docs/9.2/s
tatic/earthdistance.html
Cube based
Point based

12. SO WHAT DOES POSTGIS DO THEN?
Funny you should ask…

13. EVERYTHING
Seriously…it does pretty much
everything

14. Import and Export Data
• Import CSV
• Import/export with GDAL (Geospatial Abstraction
Library)
– Shapefiles
– OGR
– Geospatial vector data files
– OpenStreetMap data (openstreetmap.org)
– Raster datasets
• Import OGR files
• ETL migration tools
– GeoKettle

15. GIS Desktop Software
Open Source
• OpenJump
• QuantumGIS
• uDig
• GvSig
• OrbisGIS
• PostGIS Viewer
• pgAdmin plugin
Commercial
• CadCorp SIS
• Manifold.net
• MapInfo Professional
• AutoCAD
• ESRI ArcGIS

16. Mapping Servers Integration
• Mapserver
• GeoServer
• Deegree
• QGIS Server
• MapGuide

17. Data: OpenStreetMap

18. Data: US Census

19. Data: WorldClim

20. US Geological Survey

21. Natural Earth

22. MaxMind GeoIP
Web Services / API
Constantly Updated Databases
Free and Paid Versions
Check your IP to try it out
https://www.maxmind.com/en/locate
_my_ip

23. Working with Data
• Datatypes
– Geography
• Ellipsoidal spatial data
– Geometry
• Planar spatial data
• Indexes
• Topology
• Spatial Joins
• 3D
– Mapping (building, etc)
– Image generation
• pgRoute
– Generate driving route
• Generate raster images from SQL
queries
• Spatial Relationship Functions
– ST_Contains
– ST_Covers
– ST_Crosses
– ST_DWithin
– ST_Intersects
– ST_Distance
• Clustered Queries for Huge
Datasets

24. Fun data tricks
• Use a TRIGGER to populate a geographic data
column for transparent indexing
• Create a Geospatial View
• Use table inheritance to centralize
commonality among different data types
– Geographic Data
– Search Data

25. AR PostGIS Adapter
Migrations
create_table :locations do |t|
t.column :shape1, :geometry
t.geometry :shape2
t.line_string :path, :srid => 3785
t.point :lonlat, :geographic => true
t.point :lonlatheight, :geographic => true, :has_z => true
t.index :lonlat, :spatial => true
end
Datatypes
:geometry -- Any geometric type
:point -- Point data
:line_string -- LineString data
:polygon -- Polygon data
:geometry_collection -- Any collection type
:multi_point -- A collection of Points
:multi_line_string -- A collection of LineStrings
:multi_polygon -- A collection of Polygons
ActiveRecord
Location.where(:lonlat => 'POINT(-122 47)').first
Location.where("ST_Distance(latlon,
'POINT(-122.330779 47.604828)') < 10000")
scope :distance_from, ->(lat, lon, dist) do
where(“ST_Distance(latlon, ‘POINT(? ?)’) < ?, lat, lon, dist)
end
Location.where("ST_Intersects(latlon,
'POLYGON((
-122.19 47.68,
-122.2 47.675,
-122.19 47.67,
-122.19 47.68))')")
https://github.com/rgeo/active
record-postgis-adapter
Features
• Uses Rgeo gem
• Spatial Migrations
• Spatial Datatype
• Spatial Queries
• Create / Update PostGIS DB
• Support central schema

26. Assignment 2
• Refine and improve your application
• Add authentication
• Add authors (or some type of user) to created data
• Display author info on your data
• Implement simple_form somewhere
• Add a new validation rule to a model
• Add a page to show related data for an author
• Use slim (or haml) to create one of your views
• Add a BASIC geographic capability (optional)
– Use your own discretion for how deep you go
– Suggestions / Ideas
• Geocode user IP addresses to get city/state/zip info
• Add address fields to your data type to make it geographically relevant
• Use a distance filter in search