We explain you three problems the Postgres SQL extention Postgis solves (Geometric data storage, Spatial operators, Spatial index)

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