↖ Fixing Polygons in OSM

Getting Started Fixing Polygons in OSM

There are many ways of helping with this effort depending on your OSM skill level and time.

The priority for the following jobs is specified according to the visibility of the problems on the map: The priority "High" is for larger (multi)polygons such as forests that can possibly affect a large map area. "Low" is used for problems that are invisible or nearly invisible on usual maps. "Medium" is for everything in between, such as buildings, etc.

Using Maproulette

We are creating several Maproulette challenges for different skill levels, regions, and problems. They will be rolled out piece by piece. We are starting with simpler ones and build up towards the more complex problems.

Inner ways with same tags as multipolygon relation

Difficulty level: Medium

Priority: Medium

Challenge started: 2017-05-13

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:

You can take a look at all completed challenges.

Using the OSM Inspector

The Areas View in the OSM Inspector show a lot of different information about broken areas. It is a great tool for the advanced mapper, but can be daunting for the beginner. Old-style multipolygons do not show up in this view, because it would be too much data.

Fixing multipolygons in South Korea

Difficulty level: Medium

Priority: High

Challenge started: 2017-03-29

Description: South Korea has a lot of broken multipolygons. The problems include self-intersections, overlapping areas, and other problems, mostly on forest and other landuse polygons. The problems are too dense to fix using Maproulette.

To work on this: Go to the OSM Inspector and look at South Korea. Choose a random starting point, load the area into JOSM and start fixing problems. Upload often to minimize duplicate work.

You can load the OSM Inspector Area view into JOSM as a background layer to simplify this. In JOSM, open the menu "Imagary -> Imagery preferences", then find "OSM Inspector: Area" in the "Menu Name" column in the table. Click on it and then the "Activate" button below the table and close the dialog with "OK". You can now choose "OSM Inspector: Area" from the "Imagery" menu whenever you want to add the layer. The layer is transparent, so you can use it together with a satellite image layer.

Go to OSMI (todo)

Fixing duplicate nodes

Difficulty level: Easy

Priority: Low

Challenge started: 2017-02-23

Description: One very simple task is to fix duplicate nodes using OSMI and JOSM. Duplicate nodes are two nodes at the same position or one node that is in a way twice.

To work on this: Go to the OSM Inspector and only activate the duplicate nodes layers. Find an area you want to fix with lots of orange dots and load it into JOSM (using the edit button with the little "J" in it). Activate the validator in JOSM and run it. Click on the "Mixed type duplicated nodes" warning and then the "Fix" button to fix them.

Go to OSMI (todo)

Fixing old-style multipolygons with JOSM

Cleanup of all the old old-style multipolygons is done. New ones will occasionally be created by editors/mappers who don't know yet how to correctly map multipolygons. So some cleanup might still be necessary now and then.

Fixing old-style multipolygons isn't very difficult with JOSM. Look at this step-by-step description which also has a lot of handy "productivity" tips.