Kaart: Multipolygons

Introduction

Multi-polygons are used to represent various complex areas that have holes or islands in them or are made using multiple line features. They are commonly used for features like forests, coastlines, and buildings.

Prerequisites

Must have a solid understanding of relations, geometry, tagging, etc. as well as a good understanding of ID Editor or JOSM.

Skill Instruction

Before you start adding and modifying multi-polygon relations you first need to learn how the relation works and how to use the tools to modify the relation.

Parts of the Relation

Every multi-polygon relation has these parts:
Tag	Defining features that tell you what the function of the relation is. Every relation must a type=* tag.
Members	The individual ways and areas that define the multi-polygon.
Roles	Members may be give a role to define their function or to give more detail. Multi-polygons only have two roles: Outer: These make up the rings of the multi-polygon. Inner: These make up the inner rings of the multi-polygon(if any) and must be completely inside the outer ring.

The Relation Menu

The relation menu is where you will make most of the changes to the multipolygon. This menu has various tools that help you easily modify things like the tags and members of the relations.

There are three parts to the relation menu:

• Tags and Members
• Parent Relations
• Child Relations

Tags and Members

The tags and members section is where you'll make changes to the relation. This section is broken up into three parts: tags, members and selection.

Tags

This section is where you will add/modify/delete the tags of the multipolygon to further define what it is, what it's called, etc.

• Every relation must have a type=* tag to define the relation. In this case it will be type=multipolygon.
• Other common tags include: natural=*, landuse=*, building=*, highway=pedestrian, etc.
  • Note: The relation must have at least one tag to describe the feature. In some cases, you may need to create a separate multipolygon as the addition of other informative tags may have conflicting interpretations.

Tools: There are a few basic tools you can use to update the tags for the relation.

These include:
	Add tag You can also add a new tag by clicking on a blank space at the bottom of the tag table.
	Delete the selection in the tag table
	Paste tags

Members

This section is where you can modify the order of the various members, delete members and give the members a role(as needed). This is also where you can see the whole relation and determine if it needs to be fixed/modified.

Note: There isn't a limit on how many members a multipolygon can have. The order of the members also doesn't matter, but it is good practice to keep the member list in order so the relation is easier to maintain.

Tools: There are multiple tools to help you edit the members of a relation.

These include:
	Move the currently selected member(s) up/down.
	Edit the relation the currently selected relation members refers to. This applies to parent relations that have multiple child relations in them.
	Remove the currently selected member(s) from this relation.
	Sort the relation members. This will organize the members based on the order the members occur in OSM. If there are duplicate members this may cause breaks in the relation.
	Sort the selected relation members and all below. If there are duplicate members this may cause breaks in the relation.
	Reverse the order of the relation members. You can also do this with a selection of members.
	Download all incomplete members.
	Download the selected incomplete members.
	Apply role. Applies a role to the currently selected members.

Selection

This section is where you can add new members to the relation. These are ways/nodes that you have selected to help complete the relation.

Tools: There are multiple tools available to help you add your selection to the relation.

These include:
	Add all objects selected in the current dataset before the first member.
	Add all objects selected in the current dataset before the first selected member.
	Add all objects selected in the current dataset after the last selected member.
	Add all objects selected in the current dataset after the last member.
	Select relation members which refer to objects in the current selection.
	Select objects for selected relation members.
	Remove all members referring to one of the selected objects.

Member Colors

Members of the relation may have a different color to help you know more about that member.

These colors include:
White	This member does not have any duplicate members and is not currently selected in OSM or the relation menu.
Yellow	This is the feature that is currently selected in OSM. This won't show in the members list unless that feature is part of the relation, but it will always be visible in the Selection list.
Red	This indicates that a member has been duplicated somewhere in the relation.
Bold Highlight	This is what you currently have selected in the relation menu. It will be darker than the other colors.

Characteristics of a Quality Multipolygon

Every multipolygon must have the following characteristics:

• The areas/ways of the relation must form one or more closed polygons.
• Inner polygons CANNOT overlap with or be connected to the outer polygons.
  • Inner polygons may share segments in some cases.
• Exactly two unclosed ways need to share the same end point to close the polygon.
  • This is only in cases where there are multiple ways being used to create the multipolygon.

How to Map

Multipolygons are relatively easy to create and work with so they can be made using ID Editor or JOSM. It is recommended to use JOSM for more complex multipolygons.

ID Editor

There are two methods to create a multipolygon using ID Editor:

• Combining features
• Manually creating the relation

Notes:

• Some feature should be drawn as a line feature instead of an area. Otherwise ID will duplicate the area features(stand alone area + multipolygon).
• You can add new features to an existing multipolygon by shift + selecting all of the features and using C to combine them.

Combining Features

This is the easiest method for creating multipolygons in ID Editor.

• This method will not work for multipolygons that use multiple ways as members.

To do this:

• Draw the outline(s) using either a line or an area.
• Draw any inner polygons within the outline using either a line or an area.
• Shift + select all of the features and use C to combine them.
  • This will autmatically apply the "outer" and "inner" roles to the members of the relation.
• Label each feature. You may have to deselect then reselect the feature first.
  • The relatioin must have a defining feature tag.
  • The outer line/inner areas/line can be defined as needed.
• Verify that all of the roles(outer/inner) are on the correct members.

Manually Creating the Relation

Manually creating the relation allows you to draw the members however you want including using multiple ways.

To do this:

• Draw the outline(s) using either a line or an area.
• Draw any inner polygons within the outline using either a line or an area.
• Shift + select all of the features then click on the + under relations at the bottom of the Edit Features menu.
• Click the dropdown on the Choose parent relation box and select new relation.
• Click on the Multipolygon option.
• Label each feature. You may have to deselect then reselect the feature first.
  • The relation must have a defining feature tag.
  • The outer line/inner areas/line can be defined as needed.
• Resolve all issues:
  • Click on each member and select set as inner/outer for each member. They will highlight blue.
• Verify that all of the roles(outer/inner) are on the correct members.

JOSM

There are three methods in JOSM you can use to create a multipolygon:

• Hotkey
• Preset
• Manually

Notes:

• You can add new features to an existing multipolygon by shift + selecting all of the features and manually adding them to the relation.
• Some features should be drawn as a line instead of an area and vice versa.

Hotkey

Use the mutlipolygon hotkey CMD + B|Ctrl + B is the fastest way to create a new multipolygon.

To do this:

• Draw the outline(s) using either a line or an area.
• Draw any inner polygons within the outline using either a line or an area.
• Shift + select all of the features and use CMD + B|Ctrl + B to combine them as a multipolygon.
  • This will automatically apply the "outer" and "inner" roles to the members of the relation.
• Label each feature. You may have to deselect then reselect the feature first.
  • The relation must have a defining feature tag.
  • The outer line/inner areas/line can be defined as needed.
  • Keep in mind what tags should be used on the feature vs. the relation.
• Verify that all of the roles(outer/inner) are on the correct members.

Preset

Using the preset is a safe way to create a new multipolygon as it will add all of the necessary tags for you.

To do this:

• Draw the outline(s) using either a line or an area.
• Draw any inner polygons within the outline using either a line or an area.
• Shift + select all of the features, then click on the multipolygon preset.
  • Presets→Relations→Multipolygon.
• Add the selected features as members of the relation and give them roles(outer/inner).
• Label each feature. You may have to deselect then reselect the feature first.
  • The relation must have a defining feature tag.
  • The outer line/inner areas/line can be defined as needed.
  • Keep in mind what tags should be used on the feature vs. the relation.
• Verify that all of the roles(outer/inner) are on the correct members.

Note: If you draw an area with a tag describing the area, that tag will NOT automatically be added to the multipolygon. It will stay on the line feature and should be moved to the relation.

Manually

Creating the relation manually requires you to know which tags/roles are needed for the relation.

To do this:

• Draw the outline(s) using either a line or an area.
• Draw any inner polygons within the outline using either a line or an area.
• Open the relation dialogue panel.
• Shift + select all of the features, then click Create new relation.
• Add the selected features as members of the relation and give them roles(outer/inner).
• Add the tag type=multipolygon.
• Label each feature. You may have to deselect then reselect the feature first.
  • The relation must have a defining feature tag.
  • The outer line/inner areas/line can be defined as needed.
• Keep in mind what tags should be used on the feature vs. the relation.
• Verify that all of the roles(outer/inner) are on the correct members.

Note: If you draw an area with a tag describing the area, that tag will NOT automatically be added to the multipolygon. It will stay on the line feature and should be moved to the relation.

Multipolygon Examples

There are many different ways and combinations to create a multipolygon. We'll cover the common ones and some of the more advanced ones.

Common Mulitpolygons

These are the most common multipolygons you will encounter. Each has a very basic concept that can be made more complex depending on the feature(s).

One Outer Ring with Multiple Inner Rings

This is the most common and simplest multipolygon.

Multiple Ways Forming an Outer/Inner Ring(s)

These types of multipolygons allow you to use more than one way to form the outer/inner ring(s). This type of tagging is primarily used to tag very large areas like coastlines or forests.

Multiple Outer Rings

This type allows you to have multiple separate polygons that are part of the same relation. This is a true multipolygon.

A Mixture of Combinations

This method allows you to combine the different types together to create more complex multipolygons. This method is typically used when you need to describe various features in an area.

The following examples have 17 individual members and 1 relation and use most of the different types.

Island Within a Hole

This type of multipolygon allows you to have islands inside a polygon.

Touching Inner Rings

This method is used when there is more than one feature within a feature.

In this example, there is a pond and farmland in the middle of a forest.

Advanced Multipolygons

Advanced multipolygons usually combine a lot of different elements/features together which may also include multiple multipolygons.

Nested Multipolygons

A nested multipolygon is a multipolygon within another multipolygon. These can have shared members as pictured below.

Relation A	Relation B
type=multipolygon, landuse=forest Outer: 1 Inner: 2 Inner: 3, natural=water	type=multipolygon, natural=water Outer: 2 Inner: 4, natural=scrub

Multiple Ways Forming Nested Multipolygons

Here is an example of one where multiple ways/features were used to create nested multipolygons.

Relation A	Relation B
type=multipolygon, landuse=forest Outer: 1 Outer: 6, boundary=administrative Outer: 9, highway=residential Inner: 2 Inner: 3, natural=water Inner: 12, highway=track	type=multipolygon, natural=water Outer: 2 Outer: 12, highway=track Inner: 4, natural=scrub

Adjacent Multipolygons and Adjacent Inner Areas

In this example you have the nested multipolygons from above with another, adjacent multipolygon that has two inner ways.

Relation A	Relation B	Relation E
type=multipolygon, landuse=forest Outer: 1 Outer: 6, boundary=administrative Outer: 9, highway=residential Outer: 15, barrier=fence Inner: 2 Inner: 3, natural=water Inner: 12, highway=track	type=multipolygon, natural=water Outer: 2 Outer: 12, highway=track Inner: 4, natural=scrub	type=multipolygon, landuse=farmland Outer: 7, boundary=administrative Outer: 15, barrier=fence Outer: 16, barrier=fence Outer: 17 Inner: 18, landuse=farmland Inner: 19, natural=water

Disjunct Outer Rings

In this example, Relation E has two additional outer rings, E2 and E3, that are separate from the main polygon but are still part of the multipolygon.

Relation A	Relation B	Relation E
type=multipolygon, landuse=forest Outer: 1 Outer: 6, boundary=administrative Outer: 9, highway=residential Outer: 15, barrier=fence Inner: 2 Inner: 3, natural=water Inner: 12, highway=track	type=multipolygon, natural=water Outer: 2 Outer: 12, highway=track Inner: 4, natural=scrub	type=multipolygon, landuse=farmland Outer: 7, boundary=administrative Outer: 15, barrier=fence Outer: 16, barrier=fence Outer: 17 Outer: 20 Outer: 21, barrier=fence Outer: 22 Outer: 23, barrier=fence Inner: 18, landuse=farmland Inner: 19, natural=water Inner: 24

Polygons Nested 4 Levels

In the following examples there are 4 levels of nested multipolygons. Some things to keep in mind for these scenarios are:

• Only the inner most areas should have tags on the feature to describe the area.
• The other closed ways should NOT have tags that describe the area. Tags can be added to define the line features.
• Use multiple multipolygons to describe each adjacent level. In other words, add the tags that describe the area to their respective relation.

Relation A	Relation B	Relation C	Relation D
type=multipolygon, landuse=meadow Outer: 1 Inner: 2	type=multipolygon, landuse=farmland Outer: 2 Inner: 3, barrier=fence Inner: 4 Inner: 5 Inner: 6, barrier=fence	type=multipolygon, landuse=forest Outer: 3, barrier=fence Outer: 4	type=multipolygon, landuse=forest Outer: 5 Outer: 6, barrier=fence Inner: 7, natural=scrub

Suggested Bookmarks

• Relation:multipolygon
• Multipolygon Examples