PostGIS and Spatial SQL
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FOSS4G refers to free and open source software for geospatial applications. Using FOSS4G provides benefits like increased flexibility, rapid innovation, lower costs, and ability to customize software to specific needs. Spatial SQL allows querying and analyzing spatial data in databases by treating geometry as another data type. PostGIS is an open source spatial database extender for PostgreSQL that allows GIS functions and spatial indexing to be used in queries. PostGIS supports common spatial functions and data types and provides better performance than desktop GIS software or file-based formats for large-scale spatial analysis and management tasks.
PostGIS and Spatial SQL
- 6. What is “FOSS4G” FREE OPEN SOURCE SOFTWARE “4” Geospatial/GIS
- 8. Why use FOSS4G Technology • Build on Open Standards so data and code are shareable and interoperable • Increases Flexibility to respond to needs • Rapid Innovation pushes Geospatial Technology forward • Core Product can be customized to your need • Lower Cost of Software Ownership • Control When Patches are Introduced
- 10. What is Spatial SQL • Just like normal SQL but with Spatial Functions • Geometry/Geography stored as a Binary Large Object (BLOB) • Spatial Data is just another column in a database • Attribution is maintained like other data within the database
- 11. Drivers • Increase in Desire for Location Data (Social Media) • Increased Use of Mobile • Big Data/Large Amounts of Unstructured Data • Increased understanding of Geography and its role in general data analysis
- 12. Databases that Support Spatial SQL • Oracle • MySQL • SQL Server (starting in 2008) • Spatial Lite • PostGRES
- 14. PostGIS verse a “Geodatabase” (Personal, File, ArcSDE) • Spatial SQL allows to query and analyze Spatial Data, a Geodatabase is just for data management – Still relies on GUI to preform analysis • Spatial SQL is build on Open Geospatial Consortium (OGC), Geodatabases are not • Spatial SQL can support a variety of applications, Geodatabases only supports desktop GIS software and proprietary Web Servers
- 15. Shapefile verses PostGIS • Shapefiles cannot support more than 70m rows • Limitations for field names • Disk Space Hogs • Difficult to share data • Limitations to Date Field name • Do not support nulls • Files that exist in folders are difficult to manage (backups,size) • Only support Spatial Tools, not BI or non Spatial software
- 16. Spatial Data Management with PostGIS • Writing SQL to query data opposed to generating new files • Increasing performance and response speeds through Indexing • PostGIS takes advantage of multiprocessing hardware • Users can access PostGIS through the network or Internet, without a specialized web viewer or desktop software • PostGIS maintains data integrity and replication • PostGIS can handle multiple users accessing the same data • Can store Spatial Data as Text (geojson, WKT) or as Binary (BLOB or WKB)
- 17. PostGIS Spatial Capabilities • Supports all Geometry Types • Point • Multipoint • Line • Linestring • Polygon • MultiPolygon • Collections • Projections • Supports all known map projections • Allows reprojection within query • Spatial Relationships • Measure • Serialize/Deserialize • Intersect • Buffer • Point n Polygon • Overlap/Touch/Cross
- 18. PostGIS Spatial Capabilities • Can import/export any Spatial Data Type • Spatial Indexing • Allows user to reduce query time
- 19. Geometry Vs. Geography • Geography is always in WGS84 • Geography has limited Spatial Functions • Geography views the world as 2D • Geography is faster for generating visualizations • Geometry allows for full analysis • Geometry allows for 3D Analysis
- 21. Metrics (Unscientific) • 400K buffers generated • PostGIS: Shorter than a ½ mile walk with “the dog” • Proprietary Desktop GIS: 4 hours • 1.5 Billion Point in Polygon Analyses • PostGIS: Shorter than a commercial free episode of “The Walking Dead” • Proprietary Desktop GIS: Kept spinning, turned off after 24 hours • 1.5 Billion Measurements • PostGIS: a bit longer than a commercial free episode of “The Walking Dead” • Proprietary Desktop GIS – Error 99999 after 3 hours of the process
- 24. Your Current Set up • “Lone Wolf” Analyst/Developer Style • PostGRES 9.5 • PostGIS 2.3.x • QGIS 2.14 – for Map Making and Visualization
- 25. Getting Comfortable With pgAdmin 4
- 30. Group By SELECT AVG(char_length(establish)), license_ty FROM liquor_licenses GROUP BY license_ty
- 31. Standard Deviation (last non GEO one I promise) SELECT AVG(char_length(establish)), STDDEV(char_length(establish)), license_ty FROM liquor_licenses GROUP BY license_ty
- 39. Exporting as Different Data Types SELECT ST_AsGeoJSON(geom) FROM floodplain_city SELECT ST_AsGML(geom) FROM floodplain_city
- 41. ST_Intersect SELECT a.strname,a.gid,a.geom, a.leftadd1,a.leftadd2,a.rgtadd1,a.rgtadd2 FROM street_centerlines a, floodplain_city b WHERE ST_Crosses(a.geom,b.geom)
- 43. ST_Within SELECT a.establish, a.license_ty,a.gid,a.geom FROM liquor_licenses a, zoning b WHERE st_within(a.geom, b.geom) AND zone_name='LOW DENSITY MIXED-USE NEIGHBORHOOD DISTRICT'
- 44. ST_Within - part 2 SELECT COUNT(a.establish), a.license_ty, b.zone_name ,a.gid,a.geom FROM liquor_licenses a, zoning b WHERE ST_WITHIN(a.geom,b.geom) GROUP BY b.zone_name, a.license_ty