OpenHistoricalMap/Boundaries

Administrative Boundaries

The boundary=administrative tag is used on relations that define an administrative area − territories recognised by governments for administrative purposes. This works rather like multipolygon – the relation consists of one or more boundary ways that must make up a closed area.

Administrative boundaries range from large groups of nation-states down to small administrative districts. An indication of their size/level of importance is given by the tag admin_level=* which takes a value from 1 to 11, as described below. Many administrative boundaries are currently also tagged with place=*, but this practice is discouraged and instead it is recommended to use border_type=*tags.

It is recommended that all boundary areas are represented by type=boundary relations. Their border ways may be left completely untagged, with only outer and inner defined as appropriate. boundary=administrative is also often duplicated on the ways that build the relation, but such tagging is optional and may be safely skipped

Locating the administrative boundary

When mapping administrative boundaries, beware of the special cases mentioned in this section.

Administrative boundary in case of disputes

With regard to boundary conflicts, please note:

• OHM follows On the Ground Rule. Boundaries recorded in OpenHistoricalMap are the ones that are the most widely internationally recognised and that best meet realities on the ground, generally meaning physical control. In areas without clearly defined borders, the line is approximate.
• It does not mean that OHM community considers specific invasions/wars/whatever that resulted in border change as good/desirable/welcome/wrong. OHM community attempts to map world as it existed, not as it should have existed.
• In some cases borders may overlap without making it an incorrect tagging. It may be result of agreement between countries to administer area together or to mark areas not controlled by any country, with both claiming it. In some countries, subnational boundaries overlap in complex ways in reality, so data consumers and quality assurance tools should not assume that an administrative boundary is a subarea of only one administrative boundary.

Administrative boundary at sea

Main article: Tag:boundary=maritimeAdministrative boundaries should only include:

• land;
• internal waters, and;
• territorial sea (often, but not always, 12 nautical miles wide (3 nautical miles pre-UNCLOS)).

Administrative boundary relations should never contain international waters. See boundary=maritime for how to map maritime zones of coastal states.

Whether territorial sea and internal waters are included in subnational administrative divisions, varies per country.

Administrative boundary formed by a river or road

Sometimes borders and rivers/roads (or other linear objects) are tagged together on one object or their nodes are glued together. It is often undesirable and problematic, as a user modifying a river or road after its geometry changes may easily also modify the border.

A border should be glued with other elements only if they are defined in such a way that if the river changes its course, the element will also change. For example, if an administrative boundary is defined by the current course of a river, then gluing would be OK. But it is really rare, and usually river-defined borders are defined by something like "the course of a river in the year 1995". This would mean that if the river's shape changed, the shape of the border would not. Moreover, gluing a boundary to a waterway=river way implies that the boundary is defined by the river's thalweg (or whatever channel the way follows), which is sometimes incorrect.

Avoiding accidental modifications

In addition to avoiding "gluing" boundaries to other elements, accidental modifications to boundaries can be further reduced through filters in editing programs.

iD

To hide boundaries in the iD editor, select the 'Map Data' icon (or use the shortcut 'U') to bring up the Map Data side-menu. Then, from the Map Features section in the side-menu, deselect 'Boundaries'.

JOSM

To hide boundaries in JOSM, refer to the official help documentation.

Super-national administrations

 To do: How to tag super-national administrations?

National

boundary=administrative
+ admin_level=2

marks country borders, such as the border between Austria and Germany. Often non independent countries are also tagged with admin_level=2 due to a lack of admin levels hierarchy available for historical concepts.

Sub-national

boundary=administrative
+ admin_level=3 to 11

marks subnational borders.

admin_level

admin_level=1 to 11 has been introduced in order that different borders can be rendered consistently among countries (doing this based on border_type would require knowledge of their hierarchy in each country).

Besides administrative boundaries, the admin_level=* tag may also be used on features tagged with government=*. The admin_level=* values described below may also apply to the capital=* tag.

Rendering

 To do: Get actual images of OHM main style

admin_level	Example rendering		admin_level	Example rendering		admin_level	Example rendering
1	(not rendered)		5	(rendered but not labeled)		9
2			6			10
3	(not rendered)		7			11	(not rendered)
4			8			12	(not rendered)

Country specific values of the key admin_level=*

When using admin_levels please refer to and apply the correct admin_level=* tag based on the values in the table below.

You can also find modern country values here, if the country is not listed below.

Homogenous empires are usually tagged as admin_level=2 but globe spanning empires are tagged as admin_level=1 with their colonies as admin_level=2.

Table : Admin_level for all countries

Empires/Unions (admin_level=1)Countries (admin_level=2		admin_level=*										Project Page
1	2	2	3	4	5	6	7	8	9	10	11
	Bangladesh											link
	Belize			districts			cities	towns	villages	neighbourhoods/hamlets
British Empire		dominions, colonies	protectorates, territories									link
		Protectorates were partially under British control and territories were mostly claimed and not administered.
	British Raj		agencies	presidencies, provinces, Princely States								link
	Denmark			regions	counties	hundreds	municipalities		cadastral communities			link
German Colonial Empire												link
	Holy Roman Empire											link
	India			states, union territories								link
	Ireland			provinces (-1672)		counties, county corporates, county boroughs		baronies, municipal boroughs, rural districts, urban districts		townlands		link
Kingdom of the Netherlands												link
Mayan Empire		city states		vassal to a city-state, kuchkabab								link
		Mayan Empire is a modern idea but historically there were only city-states
	Mongol Empire											link
	Myanmar			regions, states, union territories, self administered areas								link
	Ottoman Empire			beylerbeyliks, eyalets, vilayets	sanjaks, liwas, mutasarrifates	kazas		nahiyes				link
	Roman Empire			provinces								link
	Spain			provinces								link
Spanish Empire		Spain, viceroyalties, captaincy generals, kingdoms		provinces, intendancies, governorates		mayoralties						link
	Sweden											Stockholm County
	United Kingdom			countries								Scotland
	United States of Indonesia			states, territories, federations	federal districts, unincorporated territories							link