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*** 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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Towards an Area Datatypefor OSM
JochenTopf
Fundamental Geometry Types
Point Linestring Polygon
Point Linestring Polygon
Node Way ??
Polygon with Holes
1 outer ring, 2 inner rings
Multipolygon
2 outer rings, 2 inner rings
Definition
A polygondevides
the surface of the planetinto
two regions:
inside - outside
Definition
A polygon is usually described by its border.
The border is a bunch of lines that never intersect.
Border line direction?
Definition
A polygon is usually described by its border.
The border is a bunch of lines that never intersect.
Border line direction?
Polygons in OSM:
There Is More Than One WayTo Do It!
Polygon Type #1:Closed way
Polygon Type #1:Closed way
No holesDepends on tags...
Polygon Type #1:Closed way
highway=residential natural=wood
Linestring or polygon or maybe both...
Polygon Type #1:area=yes
highway=pedestrian highway=pedestrian area=yes
Polygon Type #2:Multipolygon Relation
type=multipolygon
Polygon Type #2:Multipolygon Relation
type=multipolygon
Can have multiple inner and outer rings.
Polygon Type #3:Boundary Relation
type=boundary
Polygon Type #3:Boundary Relation
type=boundary
Role: subarea !
Polygon Type #4:Coastline
Ways connected end-to-end.Land always on left, water always on right.
Polygon Type #5:Riverbank
waterway=riverbank
Polygon Type #5:Riverbank
waterway=riverbank
Polygon Type #5:Riverbank
waterway=riverbank
Types of Polygons
#1 Closed Ways#2 Multipolygon Relation
#3 Boundary Relation#4 Coastlines#5 Riverbanks
Problems
Which polygon type to use?(lakes?, rivers?, boundaries?)
What if several typesare in use at the same time?
Converting from one to another?
Problems withMultipolygon Relations
Tags on relation + outer ways + inner ways
Broken geometries (Self-intersections, ...)
Inner/outer mixups
Subareas
Broken Multipolygon Relations
About 2% broken, another 2% warnings
Polygons in OSM are...
difficult to understand,diffcult to edit,difficult to use .
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
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
What are we going to do about it?
A NewArea
Datatype
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)
Polygons are Problematic...
1. Because there are several ways to accomplish the same thing.
2. Because they are hard to edit and keep valid.
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.
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
Validation
On the serverIn the editor
Lightweight!?
Check only changes!
Partial download
Check locally
API
Full download of areas not always possible!
Download parts of areas in bbox+
Upload changes of areas in bbox
I think this is doable!
*Details are left as an exercisefor the reader.
Migration
1. Add support for new area type
2. Convert some areas automatically
3. Convert rest manually
4. Remove support for old areas
