↖ 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:

Duplicate segments in closed ways ( job is done)

Difficulty level: Normal

Priority: Medium

Challenge started: 2017-03-18

Challenge finished: 2017-03-26

Description: There are many cases of duplicate segments where a closed way doubles back on itself. Usually they are left over from way back before we had multipolygons or they are from mappers who don't know about multipolygon relations and are creating several outer or inner rings by "connecting" those rings with parts of a way. There are two common cases:

Other cases than this are possible, too.

Here is an illustration of the first case, where outer rings connect to other outer rings. This is either fixed by having separate closed ways (if the ways can stand by themselves, for instance if they are just forest polygons), or by creating a proper multipolygon relation (if the ways can't stand by themselves, for instance when they form two parts of an area with a common name). You have to look at the tags to decide which case you have.

And here is an illustration of the second case, where outer rings connect to inner rings. This is usually fixed by creating a proper multipolygon relation.

To fix this: The segment(s) connecting two different rings of a multipolygon are shown. Remove the connecting segment(s) and create a proper multipolygon or separate (closed way) polygons. In JOSM "Tools/Join overlapping Areas" and "Tools/Create multipolygon" can often be used to do this quickly.

The challenge has been split up very roughly by region:

Duplicate Ways ( job is done)

Difficulty level: Easy

Priority: High

Challenge started: 2017-04-18

Challenge finished: 2017-04-23

Description: Multipolygon relations can not contain the same way more than once. The relations in this challenge do.

To work on this: The line(s) shows ways that are multiple times in a multipolygon relation. This is always wrong. Load into JOSM, open the relation in the relations editor and remove one instance of the way. Check for other problems with the relation.

Open Rings ( job is done)

Difficulty level: Normal

Priority: Medium

Challenge started: 2017-03-29

Challenge finished: 2017-04-29

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. Careful, many of these are small, but some of them are huge!

To work on 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 gap or extend an existing way. Some of these need local knowledge to fix. Do not spend too much time on these tasks, if it looks to hard, just mark it as "Too hard to fix".

"Spikes" in Buildings ( job is done)

Difficulty level: Normal

Priority: Medium

Challenge started: 2017-04-27

Challenge finished: 2017-05-06

Description: Sometimes ways contain "spikes" where the way doubles back on itself. So you have a way going from node A to B to C, back to B and then on to D. Or something like it. Some of these spikes are easy to fix (just delete node C), but sometimes they are more complicated (A, B, C, B, C, D). This challenge contains about 3000 such cases around the world.

To work on this: The marker shows the tip of a "spike", the lines the extent of the spike. Remove the spike from the way either by removing the nodes or disconnecting them from the way (Alt-J in JOSM). Fix any other multipolygon or tagging problems on the way.

"Spikes" in closed ways ( job is done)

Difficulty level: Normal

Priority: Medium

Challenge started: 2017-05-07

Challenge finished: 2017-05-12

Description: Sometimes ways contain "spikes" where the way doubles back on itself. So you have a way going from node A to B to C, back to B and then on to D. Or something like it. Some of these spikes are easy to fix (just delete node C), but sometimes they are more complicated (A, B, C, B, C, D). This challenge contains about 2000 such cases around the world.

To work on this: The marker shows the tip of a "spike", the lines the extent of the spike. Remove the spike from the way either by removing the nodes or disconnecting them from the way (Alt-J in JOSM). Fix any other multipolygon or tagging problems on the way.

Inner ways with same tags as multipolygon relation ( job is done)

Difficulty level: Medium

Priority: Medium

Challenge started: 2017-05-13

Challenge finished: 2017-05-27

Description: The inner ways in a multipolygon relation must have different tags than the relation. If they have the same tag, why are they there at all? This is often a remnant of very old tagging, or it simply can be an error.

To fix this: The line shows a multipolygon relation member way that has the same tags as its relation. Look at the tags on the relation and *all* members and make sure they make sense. Outer and inner ways should either have no tags at all or tags only pertaining to those ways. The relation should only have tags pertaining to the whole multipolygon. You also have to look at the other data in the area, sometimes the problem is duplication of data.

The challenge has been split up very roughly by region. Italy and the Netherlands have a huge amount of those issues, so they get their own challenge:

Self-Intersecting Building Outlines ( job is done)

Difficulty level: Easy

Priority: Medium

Challenge started: 2017-05-27

Challenge finished: 2017-05-29

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.

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 multipolygons ( job is done)

Difficulty level: Medium

Priority: High

Challenge started: 2017-05-29

Challenge finished: 2017-06-09

Description: Multipolygon relations with self-intersections 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. 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 by difficulty:

Self-Intersecting Ways ( job is done)

Difficulty level: Easy

Priority: Medium

Challenge started: 2017-06-10

Challenge finished: 2017-06-17

Description: Areas (buildings, landuse, natural) 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 correctness of data. 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.

Same tags on member ways (Job was cancelled)

This job was cancelled. It will be restarted in a slightly different way taking different tags into account.

Difficulty level: Medium

Priority: Medium

Challenge started: 2017-06-18

Challenge cancelled: 2017-06-20

Description: Quite often some of the outer or inner ways in a multipolygon relation have the same tags as the relation itself. This is wrong and leads to wrong renderings. Note that some tags can be the same, say you have a coniferous forest with a deciduous forest in the middle. But all tags being the same doesn't make sense. (Certain tags such as "source" are ignored in this comparison.) A member way should only have the tags describing that specific way only, not anything belonging to the whole multipolygon.

To fix this: Displayed are ways that are a member of a multipolygon relation and have the same tags as the relation. Look at the tags of the relation and all member ways and figure out what's right. Look at satellite images to help guide you.

The challenge has been split up very roughly by region. There are currently only two, more are to come:

Same tags on single member way in multipolygon relation ( job is done)

Difficulty level: Medium

Priority: Medium

Challenge started: 2017-06-20

Challenge finished: 2017-06-22

Description: Quite often some of the outer or inner ways in a multipolygon relation have the same tags as the relation itself. This is usually wrong and leads to wrong renderings. Note that some tags can be the same, say you have a coniferous forest with a deciduous forest in the middle. But all tags being the same usually doesn't make sense. (Certain tags such as "source" are ignored in this comparison.) A member way should only have the tags describing that specific way only, not anything belonging to the whole multipolygon.

To fix this: Displayed are ways that are a single member of a multipolygon relation and have the same tags as the relation. Often you can just remove the multipolygon, but look at the tags of the relation and the member way and figure out what's right. Look at satellite images to help guide you.

Same tags on member way in multipolygon relation (Buildings) ( job is done)

Difficulty level: Medium

Priority: High

Challenge started: 2017-06-23

Challenge finished: 2017-06-25

Description: Quite often some of the outer or inner ways in a multipolygon relation have the same tags as the relation itself. This is usually wrong and leads to wrong renderings. Note that some tags can be the same, say you have a coniferous forest with a deciduous forest in the middle. But all tags being the same usually doesn't make sense. (Certain tags such as "source" are ignored in this comparison.) A member way should only have the tags describing that specific way only, not anything belonging to the whole multipolygon.

To fix this: Displayed are ways that are a member of a multipolygon relation of a building and have the same tags as the relation. Often you can just remove the tags from the way, but look at the tags of the relation and all member ways and figure out what's right. Look at satellite images to help guide you.

The challenge has been split up very roughly by region:

Same tags on member way in multipolygon relation (Forests) ( job is done)

Difficulty level: Medium

Priority: High

Challenge started: 2017-06-26

Challenge finished: 2017-07-01

Description: Quite often some of the outer or inner ways in a multipolygon relation have the same tags as the relation itself. This is usually wrong and leads to wrong renderings. Note that some tags can be the same, say you have a coniferous forest with a deciduous forest in the middle. But all tags being the same usually doesn't make sense. (Certain tags such as "source" are ignored in this comparison.) A member way should only have the tags describing that specific way only, not anything belonging to the whole multipolygon.

To fix this: Displayed are ways that are a member of a multipolygon relation of a forest and have the same tags as the relation. Often you can just remove the tags from the way, but look at the tags of the relation and all member ways and figure out what's right. Look at satellite images to help guide you.

The challenge has been split up very roughly by region:

Same tags on member way in multipolygon relation (Scrub) ( job is done)

Difficulty level: Medium

Priority: High

Challenge started: 2017-07-02

Challenge finished: 2017-07-03

Description: Quite often some of the outer or inner ways in a multipolygon relation have the same tags as the relation itself. This is usually wrong and leads to wrong renderings. Note that some tags can be the same, say you have a coniferous forest with a deciduous forest in the middle. But all tags being the same usually doesn't make sense. (Certain tags such as "source" are ignored in this comparison.) A member way should only have the tags describing that specific way only, not anything belonging to the whole multipolygon.

To fix this: Displayed are ways that are a member of a multipolygon relation tagged as scrub and have the same tags as the relation. Often you can just remove the tags from the way, but look at the tags of the relation and all member ways and figure out what's right. Look at satellite images to help guide you.

The challenge has not been split up:

Same tags on member way in multipolygon relation (Woods) ( job is done)

Difficulty level: Medium

Priority: High

Challenge started: 2017-07-04

Challenge finished: 2017-07-08

Description: Quite often some of the outer or inner ways in a multipolygon relation have the same tags as the relation itself. This is usually wrong and leads to wrong renderings. Note that some tags can be the same, say you have a coniferous forest with a deciduous forest in the middle. But all tags being the same usually doesn't make sense. (Certain tags such as "source" are ignored in this comparison.) A member way should only have the tags describing that specific way only, not anything belonging to the whole multipolygon.

To fix this: Displayed are ways that are a member of a multipolygon relation tagged as woods and have the same tags as the relation. Often you can just remove the tags from the way, but look at the tags of the relation and all member ways and figure out what's right. Look at satellite images to help guide you.

The challenge has been split up very roughly by region:

Same tags on member way in multipolygon relation (Water) ( job is done)

Difficulty level: Medium

Priority: High

Challenge started: 2017-07-10

Challenge finished: 2017-07-12

Description: Quite often some of the outer or inner ways in a multipolygon relation have the same tags as the relation itself. This is usually wrong and leads to wrong renderings. Note that some tags can be the same, say you have a coniferous forest with a deciduous forest in the middle. But all tags being the same usually doesn't make sense. (Certain tags such as "source" are ignored in this comparison.) A member way should only have the tags describing that specific way only, not anything belonging to the whole multipolygon.

To fix this: Displayed are ways that are a member of a multipolygon relation tagged as water and have the same tags as the relation. Often you can just remove the tags from the way, but look at the tags of the relation and all member ways and figure out what's right. Look at satellite images to help guide you.

The challenge has been split up very roughly by region:

Same tags on member way in multipolygon relation (Riverbank) ( job is done)

Difficulty level: Medium

Priority: High

Challenge started: 2017-07-16

Challenge finished: 2017-07-22

Description: Quite often some of the outer or inner ways in a multipolygon relation have the same tags as the relation itself. This is usually wrong and leads to wrong renderings. Note that some tags can be the same, say you have a coniferous forest with a deciduous forest in the middle. But all tags being the same usually doesn't make sense. (Certain tags such as "source" are ignored in this comparison.) A member way should only have the tags describing that specific way only, not anything belonging to the whole multipolygon.

To fix this: Displayed are ways that are a member of a multipolygon relation tagged as waterway=riverbank and have the same tags as the relation. Often you can just remove the tags from the way, but look at the tags of the relation and all member ways and figure out what's right. Look at satellite images to help guide you. In addition you might want to update the riverbank tag to the more current natural=water, water=river tagging.

The challenge has not been split up by region:

Same tags on member way in multipolygon relation (Meadows) ( job is done)

Difficulty level: Medium

Priority: High

Challenge started: 2017-07-24

Challenge finished: 2017-07-26

Description: Quite often some of the outer or inner ways in a multipolygon relation have the same tags as the relation itself. This is usually wrong and leads to wrong renderings. Note that some tags can be the same, say you have a coniferous forest with a deciduous forest in the middle. But all tags being the same usually doesn't make sense. (Certain tags such as "source" are ignored in this comparison.) A member way should only have the tags describing that specific way only, not anything belonging to the whole multipolygon.

To fix this: Displayed are ways that are a member of a multipolygon relation tagged as meadow and have the same tags as the relation. Often you can just remove the tags from the way, but look at the tags of the relation and all member ways and figure out what's right. Look at satellite images to help guide you.

The challenge has not been split up by region:

Same tags on member way in multipolygon relation (Farmland) ( job is done)

Difficulty level: Medium

Priority: High

Challenge started: 2017-07-27

Challenge finished: 2017-08-05

Description: Quite often some of the outer or inner ways in a multipolygon relation have the same tags as the relation itself. This is usually wrong and leads to wrong renderings. Note that some tags can be the same, say you have a coniferous forest with a deciduous forest in the middle. But all tags being the same usually doesn't make sense. (Certain tags such as "source" are ignored in this comparison.) A member way should only have the tags describing that specific way only, not anything belonging to the whole multipolygon.

To fix this: Displayed are ways that are a member of a multipolygon relation tagged as farmland and have the same tags as the relation. Often you can just remove the tags from the way, but look at the tags of the relation and all member ways and figure out what's right. Look at satellite images to help guide you.

The challenge has not been split up by region:

Same tags on member way in multipolygon relation ( job is done)

Difficulty level: Medium

Priority: High

Challenge started: 2017-08-08

Challenge finished: 2017-08-20

Description: Quite often some of the outer or inner ways in a multipolygon relation have the same tags as the relation itself. This is usually wrong and leads to wrong renderings. Note that some tags can be the same, say you have a coniferous forest with a deciduous forest in the middle. But all tags being the same usually doesn't make sense. (Certain tags such as "source" are ignored in this comparison.) A member way should only have the tags describing that specific way only, not anything belonging to the whole multipolygon.

To fix this: Displayed are ways that are a member of a multipolygon relation and have the same tags as the relation. Often you can just remove the tags from the way, but look at the tags of the relation and all member ways and figure out what's right. Look at satellite images to help guide you.

The challenge has not been split up by region: