This document discusses managing geospatial data with PostGIS. It begins with an introduction to geospatial data and its prevalence. It then defines what PostGIS is, as an extension to PostgreSQL that allows it to store and query geospatial data. It outlines the basic spatial data types in PostGIS like Point, LineString, and Polygon. It provides an example of calculating the distance between two points using PostGIS' ST_Distance function. It also discusses spatial referencing systems (SRIDs), indexing spatial data with GiST indexes, and provides examples of how to get started using PostGIS with PostgreSQL.

1. Managing GeoData
with PostGIS
Volodymyr Gamula
KhmelnytskyiPy #1

2. Agenda:
• Current situation with GeoData
• What is PostGIS?
• Spatial Data types in PostGIS?
• Trivial problem
• SRID
• Indexing
• Another ways to use PostGIS for
• How to start working with PostGIS now?
• Program interfaces
• Conclusions

3. GeoData is an information
about geographic location,
stored in a specific format that
can be used in geographic
information systems (GIS)
What is GeoData?

4. Current situation with
GeoData

5. GeoData is everywhere!

7. Suggested timeslots

8. What is PostGIS?

9. – Paul Ramsey, Chair of PostGIS Steering Committee
“It is a Relational Database System that in
addition to text and numbers and dates, it can
also index spatial objects - points, lines, and
polygons.”

10. History
• PostgreSQL: May 1, 1995
• PostGIS: April 19, 2005
• Very well tested
• Massively used in production

11. Spatial Data types in
PostGIS

12. Point
• (x, y, z) coordinates
• Represents locations such as buildings, train
stations, etc.
• Also represents GPS latitute and longitude
• POINT(-51.1231325 12.213155)

13. LineString
• Multiple points connected by straight lines
• Represents things such as roads, routes, cables,
etc.
• LINESTRING(30 10, 10 30, 30 40)

14. Polygon
• Multiple points which encloses an area
• Represents boundaries such as properties, towns,
countries.
• POLYGON(30 10, 10 20, 20 40, 40 40, 30 10)

15. Trivial problem

16. Distance between two
points

17. 2 dimensions:

18. Geographical distance:

19. What if we need to
recalculate distance for
every request?

20. Standard formula brings
a lot of complexity :(

21. So, what should we do?

22. Geohashing

25. PostGIS has a function
ST_Distance

26. ST_Distance can work with the next
types, which are basic PostGIS types:
• Geometry
• Geography

27. We should represent
(lat, lng) to PostGIS
Geography field

28. There are a lot of ways to do it:
• 'SRID=4326;POINT(83.106560 54.838971)'::geography
• ST_GeographyFromText('SRID=4326;POINT(-110 30)’)
• ST_GeomFromEWKT('SRID=4269;POINT(-110 30)’);
• ST_GeomFromGeoJSON(‚{"type":"Point","coordinates":
[-48.23456,20.12345]}')
• ST_GeomFromGML('
<gml:Point srsName="http://www.opengis.net/def/crs/EPSG/0/4326">
<gml:coordinates>45.67, 88.56</gml:coordinates>
</gml:Point>’);
• etc.

29. SRID

30. Query:

31. Why will this query be
so fast?

32. Indexes!

33. Indexes:
• B-Tree
• R-Tree
• GiST (Generalized Search Trees)

34. GiST Indexing for GeoData with
calculations

35. Another PosGIS
calculations:
• Area
• Distance
• Length
• Perimeter
• Union
• Difference
• Symmetric difference

36. How to start work with
PostGIS now?
• Install PostgreSQL
• Install PostGIS
• CREATE EXTENSION postgis;
• CREATE EXTENSION btree_gist;
• ALTER TABLE geodata_test ADD COLUMN location
geography(Point, 4326);
• CREATE INDEX ix_geodata_test_geohash ON
geodata_test USING GIST(location);

37. Program interfaces:
GeoAlchemy

38. GeoDjango

39. Conclusions

40. Thanks!
@vgamula