↖ Fixing Polygons in OSM

Several Maproulette challenges have already been done. They are linked here for reference. But there is more to do.

Self-Intersecting Building Outlines ( job is done)

Difficulty level: Easy

Priority: Medium

Challenge started: 2017-02-14

Challenge finished: 2017-02-23

Description: Building outlines made from a single way that intersects itself. Self-intersection creates invalid polygons that should be fixed. Sometimes these are not rendered. Only ways with less than 100 nodes show up.

To fix this: Remove the self-intersection. Use the aerial images to verify that there is a building. Often the intersection is due to a node near (or directly on top of) another node at one of the corners and you can simply merge those nodes.

The challenge has been split up very roughly by region:

Self-Intersecting Landuse Outlines ( job is done)

Difficulty level: Easy

Priority: High

Challenge started: 2017-02-21

Challenge finished: 2017-02-26

Description: Landuse outlines made from a single way that intersects itself. Self-intersection creates invalid polygons that should be fixed. Sometimes these are not rendered. Only ways with less than 50 nodes show up.

To fix this: Remove the self-intersection. Use the aerial images to verify that the landuse is correctly tagged. Often the intersection is due to a node near (or directly on top of) another node at one of the corners and you can simply remove one of the nodes or merge the nodes.

Go to the challenge.

Open Rings ( job is done)

Difficulty level: Normal

Priority: Medium

Challenge started: 2017-02-21

Challenge finished: 2017-03-04

Description: Multipolygon relations containing an unclosed ring. So the boundary of the (multi)polygon is not closed. These can not be rendered and must be fixed. Only relations with less than 100 nodes are show and only if the distance between the open ends is small.

To fix this: Lines show the ring with the markers at the open ends. Look at the aerial images first and determine whether the multipolygon makes sense. Often it can be removed, because there is another (complete) polygon or multipolygon that already does its job. If it can be removed, make sure to remove the multipolygon relation as well as all the member ways that are not needed for something else. If it needs to be kept, close the ring by drawing a new way over the the gap or extend an existing way. Some of these need local knowledge to fix.

Go to the challenge.

Wrong role (should be inner) ( job is done)

Difficulty level: Normal

Priority: Low

Challenge started: 2017-02-24

Challenge finished: 2017-03-07

Description: Ways that are in a multipolygon relation with the wrong role. Only roles 'inner' and 'outer' are allowed and these ways should have role 'inner'.

To fix this: This is a way that is in a multipolygon relation and the computer thinks it should have the role 'inner'. Verify that this is correct and set the right role. False-positives are possible. Sometimes the role contains some useful information that can be moved into a tag. Ways are often in multiple relations, make sure you fix the right one!

Go to the challenge.

Self-Intersecting Polygon Ways ( job is done)

Difficulty level: Normal

Priority: Medium

Challenge started: 2017-03-04

Challenge finished: 2017-03-11

Description: Building, landuse, or natural polygon outlines made from a single way that intersects itself. Self-intersection creates invalid polygons that should be fixed. Sometimes these are not rendered.

To fix this: Remove the self-intersection. Use the aerial images to verify that the way is tagged correctly. Often the intersection is due to a node near (or directly on top of) another node at one of the corners and you can simply remove one or merge those nodes.

The challenge has been split up very roughly by region:

Self-Intersecting Multipolygon Relations ( job is done)

Difficulty level: Difficult

Priority: High

Challenge started: 2017-03-11

Challenge finished: 2017-03-17

Description: Building, landuse, or natural multipolygon outlines from multipolygon relations that intersects itself. Self-intersection creates invalid polygons that should be fixed. Sometimes these are not rendered.

To fix this: Remove the self-intersection(s). Use the aerial images to verify that the relations and ways are tagged correctly. Check that the tags for the multipolygon are all on the relation, not the ways.

The challenge has been split up very roughly by region:

Ways with a single node ( job is done)

Difficulty level: Easy

Priority: Low

Challenge started: 2017-03-15

Challenge finished: 2017-03-18

Description: These are ways that contain only a single node. Sometimes the same node is in the way multiple times. Some of these will be detected as polygons, because the first and last node are the same, so they are closed ways. They contain neither a proper line geometry nor a proper polygon geometry, so they need to be removed or fixed.

To fix this: This is the location of a way containing a single node one or more times. Look at the tags and decide what to do with the way. Most can probably be deleted, but maybe the tags are still useful.

A tip: Using a JOSM filter like type:way nodes:1 OR nodes:2 makes it easier to see where the case are.

The challenge has been split up very roughly by region: