PostGIS is an open-source extension for SQL that addresses challenges in spatial data storage and querying by providing custom spatial data types and spatial operators for geometry manipulations. It integrates spatial indexes like R-trees for fast querying, improving performance for geospatial analysis. PostGIS follows the OGC's Simple Features for SQL specification, enhancing SQL capabilities with lightweight geometries and optimized indexes.

1. Why is PostGIS awesome?
Reason 1: it is open source
Kasper Van Lombeek - Forespell.com
17 / 11 / 2016 - DS Meetup Antwerp

2. First we need to understand:
Why did SQL need an extension?

3. Problem 1: data storage

4. Try to store this rectangle in a db
A db that allows only atomic data
points.
P1 P2
P3P4

5. Lets tryPid X Y
P1 0 0
P2 0 1
P3 1 1
P4 1 0
Table 1: points
Eid Pid
E1 P1
E1 P2
E2 P2
E2
…
P3
…
Table 3: Starts_or_ends
Eid Length
E1 1
E2 1
E3 1
E4 1
Table 2: Edges
P1 P2
P3P4
E1
E2
E3
E4
Rid Eid
R1 E1
R1 E2
R1 E3
R1
…
E4
…
Table 4: Boundary
Rid Rname
R1 UnitSquare
Table 5: Rectangle

6. Lets try storing all the neighbourhoods
in Belgium?

7. Solution: SQL 3 custom spatial data types
PostGIS follows the Simple Features for SQL specification from the Open Geospatial
Consortium (OGC).

8. Problem 2: querying the
database

9. How to query our db?
Describe in words how to query the
points within the rectangle.

10. What about a more complex shape?
Would your query still work?

11. Solution: spatial operators
Provided by GEOS - Geometry Engine, Open Source

12. Problem 3: querying the
database fast

13. In which area do we have most
bicycle thefts?

14. Need for an index

15. Solution: spatial index
R-tree implementation of bounding boxes of geometries

16. These three solutions are integrated
in PostGIS
- Geometry types for Points, LineStrings, Polygons, MultiPoints, MultiLineStrings, MultipPolygons and
GeometryCollections.
- Spatial predicates for determining the interactions of geometries using the 3x3 DE-9IM (provided by the GEOS
software library).
- Spatial operators for determining geospatial measurements like area, distance, length and perimeter.
- Spatial operators for determining geospatial set operations, like union, difference, symmetric difference and
buffers (provided by GEOS).
- R-tree-over-GiST (Generalized Search Tree) spatial indexes for high speed spatial querying.
- Index selectivity support, to provide high performance query plans for mixed spatial/non-spatial queries.
- For raster data, PostGIS WKT Raster (now integrated into PostGIS 2.0+ and renamed PostGIS Raster)
- The PostGIS implementation is based on "light-weight" geometries and indexes optimized to reduce disk and
memory footprint. Using light-weight geometries helps servers increase the amount of data migrated up from
physical disk storage into RAM, improving query performance substantially.
- PostGIS is registered as "implements the specified standard" for "Simple Features for SQL" by the OGC.[2]
PostGIS has not been certified as compliant by the OGC. For the OGC's definition of compliant, see What does
"Compliant" mean?.
Source: wikipedia

17. Demo in IPython notebook