Open Historical Map

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Ohm logo small.png

Open Historical Map (OHM) ( is a site that uses the OSM software stack as a foundation for building an open source, user-editable historical map. This project's goal is to create the world's most universal, detailed, and out-of-date map. OHM will focus on the mapping the geo-objects that OSM is great at mapping - shorelines, political boundaries, buildings, ways, and points of interest. Future and other efforts may engage in discussing historical actions, events, people, and movable items.

Note: As opposed to other projects such as OpenSeaMap, OHM makes use of its own database independent of OSM.

Open Historical Map/FAQ

OHM-Related Resources

Editing Maps in OHM

Because OHM is a separate application from OSM, users must create OHM accounts to edit maps in OHM.

In-browser editing: OHM supports both iD and Potlatch.

JOSM: you must change the API settings in JOSM preferences to set the OHM server API connection parameter (uncheck the default): use Please note, https: and not http.

JOSM OHM Preferences.png

You may also edit using JOSM by choosing "Edit with Remote Control" in the dropdown menu next to the "Edit"-button on the website. Ensure that Remote Control is enabled under Preferences in JOSM and that JOSM is running. The api will be connected automatically.

How to map

Note on Transferring Data from OpenStreetMap

Transferring data from OSM is strictly discouraged unless you are the author and sole editor of the map data in OSM. There are many reasons for this, but the primary reason is copyright-related. We would like to preserve the right to distribute as much of OHM's data as possible under the CC0 license or to distribute OHM extracts with the CC0 license, which is incompatible with OSM's OdbL license. To be clear, as of June 2019, there is OSM-derived data in OHM at this time and the markings on the OHM website are incorrect. The OHM community is working to address this.

HIGHLY Recommended Tags

start_date=* and end_date=*

Apply a start date and/or end date to the feature. The format is ISO 8601 format YYYY-MM-DD.

This "qualifies" the mapping data as historical and will make it viewable only during that time period.

If you do not know the actual day, you can just add the year, e.g., start_date=1925.


  • 1901-01-20
  • 1902-12
  • 1878
  • 1900..1925 (between 1900(-01-01) and 1925(-12-31))
  • 1900-06..1901-04-23
  • before 1910-01-20 (before a specific date - possibly when a photo was taken)

There are JavaScript modules for parsing these values and translating into a human readable version, and generating queries for Overpass.


Always add the source=*-tag. Ideally, this will include a URL directly to a source map.


  • Ribeiro's_World_Map:
  • 1853 Mitchell Map of Asia:


Please tag your map information at the object level. It is highly recommended to license your data as CC0.


Regardless of whether your license requires attribution or not, you can put an attribution here. Of note, OHM is attempting to tag attribution at the object level (POIs, ways, relations) rather than at the changeset level. This is fundamentally different from OSM's approach, which recommends putting attribution at the changeset level. It is expected that any particular changeset might involve a set of objects with multiple attributions that should all be: a) exposed to the editor directly, and b) preserved across changesets.


Wikipedia is a great source of historical information and a great source of ideas for what could be mapped in OHM. Be sure to link to a related article wherever possible. And, be sure to use the language prefix when using this tag, e.g. wikipedia=en:Carcassonne.


This will link your OHM data to a particular wikidata Q code. e.g. wikidata=Q6582.

Tracing from imagery

An example URL for a Tile Server is The URL template from that source would be{z}/{x}/{y}.jpg.

JOSM - works with WMS Server, Tile Servers and local images. See JOSM Imagery Guide for more information.

iD Editor - open the layers panel, click "Custom" and paste in a valid Tile URL template.

Further notes

For further in depth tagging of features, you may consider Comparison of life cycle concepts, in particular the date namespace suffix and the lifecycle prefix.

Google Summer of Code proposal

A number of projects that are in the Wikimaps, OSM, OHM, Wikimedia area would benefit from the temporal flexibility in the OSM tool stack. This would allow us to use data across projects, using layers from multiple sources at different time periods. These projects include:

  • Design a how-to map.
  • Enhance iD and The Rails Port so that a JavaScript time/date slider can be added to control the time period that is of interest.
  • Enhance iD and The Rails Port so that meta-data hooks are added to the code that allow for custom deployments of both software. The intent is to support their use as dedicated user interfaces to certain applications (such as medieval walking path editing) while still using a generic data source.

Using the data

There are a variety of ways to use OpenHistoricalMap Data.

For smallish scale it is possible to download data using JOSM. Two alternatives now exist for larger volumes of data or larger areas:

See also these pages for the legal attributions:

Short-term plans

Keys proposed

Related OSM Projects


OHM-related mashups