A travellers guide to mapping technologies in django
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The document is a comprehensive guide on mapping technologies in Django, covering topics such as the fundamentals of mapping, storing and querying geospatial data, and displaying this data using various web mapping libraries. It emphasizes the importance of understanding geographic coordinate systems, data formats, and the functionality provided by Django's GIS capabilities. Additionally, the document explores future directions for geospatial technologies, highlighting mobile and augmented reality trends while encouraging the use of existing libraries and careful consideration of data sources and licenses.
![SIMPLE EXAMPLE
<!DOCTYPE html>
<html>
<head>
<link rel="stylesheet” href="https://unpkg.com/leaflet
@1.3.3/dist/leaflet.css" />
<script src="https://unpkg.com/leaflet@1.3.3 /dist/leaflet.js"></script>
</head>
<body>
<div id="map" style="width: 600px; height:
400px;"></div>
<script>
var map = L.map('map').setView([-33.8733, 151.1991],
19);
L.tileLayer(
'https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png’
,{attribution: 'OpenStreetMap contributors’}
).addTo(map);
L.marker([-33.8733, 151.1991]).addTo(map)
.bindPopup('You are here.')
.openPopup();
</script>
</body>
</html>](https://image.slidesharecdn.com/atravellersguidetomappingtechnologiesindjango-180827010519/85/A-travellers-guide-to-mapping-technologies-in-django-38-320.jpg)
A travellers guide to mapping technologies in django
- 1. A TRAVELLER'S GUIDE TO MAPPING TECHNOLOGIES IN DJANGO Anthony I. Joseph DjangoConAU 2018 24 August 2018 anthony.djangoconau@fastmail.com linkedin.com/in/anthony-joseph/ This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Australia License.
- 3. TALK OVERVIEW 1. Mapping Fundamentals 2. Storing Geospatial Data 3. Querying Geospatial Data 4. Displaying Geospatial Data 5. Future Directions 6. Q&A
- 5. THE BASICS Sydney Opera House Latitude: -33.8566 Longitude: 151.21507 But what is a co-ordinate?
- 6. A GEOGRAPHIC COORDINATE SYSTEM 3D Spherical Surface Latitude/Longitude Angles from a centre point WGS84 World Geodetic System SRID: 4362
- 7. GEOGRAPHIC COORDINATE SYSTEMS Advantages No distortions Represent any point Disadvantages Complicated distance/area calculations Display 3D point in 2D media? Image source: https://desktop.arcgis.com/en/arcmap/10.3/guide- books/map-projections/about-geographic-coordinate-systems.htm
- 8. PROJECTED COORDINATE SYSTEMS Examples: Web Mercator GDA94 Geocentric Datum of Australia 1994 Advantages: Great for display Great for analysis* Disadvantages: Distorted area/distance/shape Image source: https://www.xkcd.com/977/
- 9. COMMON DATA FORMATS Vector Raster Image Sources: - https://twitter.com/PSMA/status/1031799625831854080/photo/1 - http://www.ga.gov.au/scientific-topics/national-location-information /digital-elevation-data
- 10. COMMON DATA TYPES: POINTS
- 11. COMMON DATA TYPES: (POLY)LINES Data source: https://www.smh.com.au/national/nsw/sydney-s-latte-line exposes-a-city-divided-20180327-p4z6et.html
- 12. COMMON DATA TYPES: POLYGONS Data source: https://www.psma.com.au/products/administrative- boundaries
- 13. COMMON DATA TYPES: MULTI-POLYGONS Data source: https://www.psma.com.au/products/administrative- boundaries
- 14. ANALYTICAL CONCEPTS Geocoding: “130 George Street, Sydney” -33.8599, 151.2090 Reverse Geocoding: -33.8599, 151.2090 “130 George Street, Sydney” “Museum of Contemporary Art” …
- 15. ANALYTICAL CONCEPTS Geolocation IP Latitude/Longitude Autocomplete Use geolocation to suggest address
- 16. ANALYTICAL CONCEPTS Routing: “Opera House” “Museum of Contemporary Art” by walking Transportation modes: Walking Public Transport Cycling Driving/taxi/ridesharing
- 17. SPATIAL ANALYSIS Image source: - https://www.mapbox.com/use-cases/data- visualization/ - https://www.smh.com.au/national/nsw/sydney-s- latte-line-exposes-a-city-divided-20180327- p4z6et.html
- 18. SPATIAL ANALYSIS - ISOCHRONES Image source: https://app.traveltimeplatform.com
- 19. 2. STORING GEOSPATIAL DATA
- 20. GIS DATA SOURCES Web services: Web Map Service (WMS) Web Coverage Services (WCS) Open Geospatial Consortium File formats: Well-known text (WKT) Keyhole Markup (KML) GeoJSON ESRI ArcGIS Shapefiles MapInfo TAB files
- 21. DATABASE ENGINES GIS extensions to database systems OpenGIS® Implementation Standard for Geographic information PostgreSQL + GIS = PostGIS SQLite + GIS = Spatialite …MySQL/MSSQL/OracleDB …MongoDB
- 23. DATABASE FIELDS DATA TYPE FIELD TYPE Points PointField/MultiPointField Lines LineStringField/ MultiLineStringField Polygons PolygonField/MultiPolygonField Source: https://docs.djangoproject.com/en/2.0/ref/contrib/gis/model-api
- 24. MAP PROJECTIONS / SPATIAL REFERENCES Default: WGS84 SRID: 4362 geography=True Improves query performance on distance queries from django.contrib.gis.db import models class Suburb(models.Model): postcode = models.CharField(max_length=4) boundary = models.PolygonField( geography=True, # defaults srid=4326, spatial_index=True, )
- 25. SPATIAL REFERENCE SYSTEMS Data often in WGS84 May get data in other reference systems Convert between systems: Reproject – ogr2ogr Check the metadata!
- 26. SPATIAL INDEXES Regular DB Indexes (B-trees) index=True Spatial Indexes (R-tree variants) spatial_index=True Image sources: https://ieftimov.com/postgresql-indexes-btree http://revenant.ca/www/postgis/workshop/indexing.html
- 27. 3. QUERYING GEOSPATIAL DATA
- 28. QUERYING DATA qs = Model.objects.filter( <field>__<lookup_type>=<param> ) Complete list: https://docs.djangoproject.com/en /2.0/ref/contrib/gis/geoquerysets/
- 29. QUERYSETS: POINT IN POLYGON Example model Example query class Suburb(models.Model): postcode = models.CharField() boundary = models.PolygonField() pnt = GEOSGeometry('POINT(151.178 -33.884)’, srid=4326) qs = Suburb.objects.filter( boundary__contains=pnt)
- 30. QUERYSETS: WITHIN DISTANCE (2KM) Example model Example query class Store(models.Model): name = models.CharField() location = models.PointField() from django.contrib.gis.measure import D pnt = GEOSGeometry('POINT(151.196 -33.870)’, srid=4326) qs = Store.objects.filter( location__dwithin=(pnt, D(m=2000))) )
- 31. QUERYSETS: SORT BY DISTANCE Example model Example query class Store(models.Model): name = models.CharField() location = models.PointField() from django.contrib.gis.db.models.functions import Distance usr = GEOSGeometry('POINT(151.178 -33.884)’, srid=4326) qs = Store.objects.annotate( distance=Distance(‘location',listing.point) ).order_by('distance') 1 2 3
- 33. 4. DISPLAYING GEOSPATIAL DATA
- 34. REQUIREMENTS >Spatial data (already have this!) >A web mapping library >Base maps
- 35. WEB MAPPING LIBRARIES >Javascript-based >Examples: >Openlayers >Leaflet/Mapbox >Google Maps >Mobile SDKs for native apps
- 36. BASE MAPS >Tile-based imagery >Graphics: Google Maps / Mapbox / OpenStreetMap / ArcGIS … >Satellite imagery: DigitalGlobe / Nearmap / US Gov (NASA etc) >URL formats: >https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png
- 37. BASE MAP EXAMPLES Apple Maps Google Maps (Satellite) Google Maps HERE Maps Mapbox Maps
- 38. SIMPLE EXAMPLE <!DOCTYPE html> <html> <head> <link rel="stylesheet” href="https://unpkg.com/leaflet @1.3.3/dist/leaflet.css" /> <script src="https://unpkg.com/leaflet@1.3.3 /dist/leaflet.js"></script> </head> <body> <div id="map" style="width: 600px; height: 400px;"></div> <script> var map = L.map('map').setView([-33.8733, 151.1991], 19); L.tileLayer( 'https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png’ ,{attribution: 'OpenStreetMap contributors’} ).addTo(map); L.marker([-33.8733, 151.1991]).addTo(map) .bindPopup('You are here.') .openPopup(); </script> </body> </html>
- 39. SIMPLE EXAMPLE Web maps automatically reproject: >from WGS84 (geographical coordinate system), >to Web Mercator (projected coordinate system)
- 40. FORMS API DATA TYPE FIELD TYPE Points PointField/MultiPointField Lines LineStringField/ MultiLineStringField Polygons PolygonField/MultiPolygonField Source: https://docs.djangoproject.com/en/2.1/ref/contrib/gis/forms-api/
- 42. RELATED TECHNOLOGIES Offline analysis: QGIS/ArcGIS Tableau/PowerBI GeoMesa: big data for spatial WebGL Maps Mobile: 3D graphics (Unity) Augmented/Virtual Reality Image source: https://www.mapbox.com/augmented-reality/
- 43. DATA SOURCES Open data data.gov.au Government data PSMA: psma.com.au Buildings API Commercial data MaxMind/ip2location Check licences!
- 44. NEW AUSTRALIAN DATUM Currently use GDA94 (EPSG 4939) Geosciences Australian developing GDA2020 (EPSG 7844) Affects Australian government data May need to reproject data Image source: http://www.ga.gov.au/scientific- topics/positioning-navigation/datum- modernisation
- 45. KEY TAKEAWAY POINTS The official docs are great: don’t forget to use them! Make use of existing libraries/3rd party services: “don’t roll your own crypto”! Be careful of: • coordinate systems • licences • coverage Geospatial analysis is a lot like statistics: easy to do something that looks correct, but has underlying issues. Question assumptions and check metadata