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# Towards an area datatype for OSM - State of the Map 2013

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*** Presented by Jochen Topf at State of the Map 2013 …

*** Presented by Jochen Topf at State of the Map 2013
*** For the video of this presentation please see http://lanyrd.com/2013/sotm/scpkrr/
*** Full schedule available at http://wiki.openstreetmap.org/wiki/State_Of_The_Map_2013

OpenStreetMap currently does not have a polygon or area data type. Instead areas are usually modelled as closed ways or multipolygon relations (plus some other approaches for special cases). This diversity in solutions for essentially the same problem makes editing and using OSM data much harder than it needs to be. Especially multipolygon relations are difficult to work with and they are quite brittle, leading to a lot of broken data in OSM. The talk will show the problems we currently have when editing and using OSM data. It will describe approaches for a solution with their advantages and disadvantages and the changes necessary to the core database, editors, and applications using OSM data.

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### Transcript

• 1. Towards an Area Datatype for OSM Jochen Topf
• 2. Fundamental Geometry Types
• 3. Point Linestring Polygon
• 4. Point Node Linestring Way Polygon ??
• 5. Polygon with Holes 1 outer ring, 2 inner rings
• 6. Multipolygon 2 outer rings, 2 inner rings
• 7. Definition A polygon devides the surface of the planet into two regions: inside - outside
• 8. Definition A polygon is usually described by its border. The border is a bunch of lines that never intersect. Border line direction?
• 9. Definition A polygon is usually described by its border. The border is a bunch of lines that never intersect. Border line direction?
• 10. Polygons in OSM: There Is More Than One Way To Do It!
• 11. Polygon Type #1: Closed way
• 12. Polygon Type #1: Closed way No holes Depends on tags...
• 13. Polygon Type #1: Closed way highway=residential natural=wood Linestring or polygon or maybe both...
• 14. Polygon Type #1: area=yes highway=pedestrian highway=pedestrian area=yes
• 15. Polygon Type #2: Multipolygon Relation type=multipolygon
• 16. Polygon Type #2: Multipolygon Relation type=multipolygon Can have multiple inner and outer rings.
• 17. Polygon Type #3: Boundary Relation type=boundary
• 18. Polygon Type #3: Boundary Relation Role: subarea ! type=boundary
• 19. Polygon Type #4: Coastline Ways connected end-to-end. Land always on left, water always on right.
• 20. Polygon Type #5: Riverbank waterway=riverbank
• 21. Polygon Type #5: Riverbank waterway=riverbank
• 22. Polygon Type #5: Riverbank waterway=riverbank
• 23. Types of Polygons #1 Closed Ways #2 Multipolygon Relation #3 Boundary Relation #4 Coastlines #5 Riverbanks
• 24. Problems Which polygon type to use? (lakes?, rivers?, boundaries?) What if several types are in use at the same time? Converting from one to another?
• 25. Problems with Multipolygon Relations Tags on relation + outer ways + inner ways Broken geometries (Self-intersections, ...) Inner/outer mixups Subareas
• 26. Broken Multipolygon Relations About 2% broken, another 2% warnings
• 27. Polygons in OSM are... difficult to understand, diffcult to edit, difficult to use.
• 28. Some Numbers... 110 million (closed way) polygons 90 million are buildings 72 million have 6 points or less 900,000 area=yes 750,000 natural=coastline (31 million nodes) 260,000 waterway=riverbank
• 29. Relations 1,000,000 type=multipolygon 200,000 type=boundary For together >2 million (multi-)polygons 1,100,000 landuse/natural=* 240,000 boundary=administrative Largest multipolygon 300,000 points
• 30. What are we going to do about it?
• 31. A New Area Datatype
• 32. What Should it Look Like? Referencing nodes? (Like a way?) (What about huge areas?) Referencing ways? (A bit like MP relations?) (What about small areas?) Not referencing anything, coordinates inside? (Like Simple Feature)
• 33. Polygons are Problematic... 1. Because there are several ways to accomplish the same thing. 2. Because they are hard to edit and keep valid.
• 34. Polygons are Problematic... 1. Because there are several ways to accomplish the same thing. → One area datatype 2. Because they are hard to edit and keep valid.
• 35. Polygons are Problematic... 1. Because there are several ways to accomplish the same thing. → One area datatype 2. Because they are hard to edit and keep valid. → Let the computer do the checking
• 36. Validation In the editor On the server Partial download Lightweight!? Check locally Check only changes!