Open Historical Map

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Open Historical Map (OHM) is a site that uses the OpenStreetMap (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 This project's goal is to create the world's most universal, detailed, and out-of-date map. It's almost like taking all of the old maps and historical maps we can find and combining them into one. 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.

OHM Contributors include members of the OSM community, academic dataset providers, historical societies, digital humanities students and faculty, armchair historians, open data providers, open data enthusiasts, and any number of other map data creators. This is not to discount the innumerable number of software developers who have contributed time and energy to the rich set of OSM software and tools that also make OHM possible, but they are not included, in this strictest sense in "OHM Contributors," which refers to data contributors.

(all OHM project subpages under this page)

Land acknowledgment

[THIS IS A DRAFT - input is welcome]

"We must also remember that our history includes those who were kidnapped and brought here in the name of colonization and imperialism. We need to learn, protect, and honor the history and people of the places we each individually live in. We honor the lives of all who endured and continue to endure in the face of settler colonial oppression and white supremacy." - Excerpt from the Art Libraries Society of North America's Virtual Conference 2020 Land Acknowledgement.

While mapping history, we must all remember the biases and perspectives of the mappers when they portrayed indigenous lands and people. When using technology, we must all remember the biases inherent not just in our sources, but in our tools, our taxonomies, and our perspectives. The OHM Community asks all of its participants to honor and respect the history of indigenous people, to recognize that a place's history rarely began with exploration or colonial settlement, and to be open to questions about inclusivity.

OHM Code of Conduct

OHM's Community is a civil, sharing, and respectful group. That said, codifying what that means is important and we have done so. Read the details of the OHM Code of Conduct here.

First-time visitors

Newcomers - if you've made it this far, you should know a little about who and what OHM is, that we care about acknowledging indigenous people, and have basic rules for decent, humane interaction.

If you like what you've read, please visit the OHM Basics page first.

OHM Web Services

We have a range of web services available for OHM, as well as staging environments for most of them.

Wondering if there's an outage? Check our system status page.

Production Services

This is what everyone should use for day-to-day work.

Web GUI tools

Command Line Tools

Staging Services

These are used when deploying new features or tracking down bugs.

Web GUI tools

Command Line Tools

OHM projects

Mappers working in OHM are encouraged to create project pages describing their work. This can provide context and framing that are not practical in the map itself and provide details on sourcing and source choices that don't fit easily into source=*.

Projects are grouped here: OHM Projects.

OHM resources

Please find sources to meet your project needs within the OHM Resources page. This page provides a place to list map, imagery and documentary sources that are appropriately licensed for use in the OHM project.

Fast answers for your OHM questions

More detailed, related, and technical sites

OHM Streams

Various OHM contributors livestream. The current schedule may be found at Open Historical Map/OHM Streams.


This page of the OHM wiki is currently being revised. Much has been moved to Open Historical Map/OHM Basics. Look there for an introduction to OHM editing.

Information about using historic imagery and maps with OHM is being put in the new Open Historical Map/Imagery page.


For those familiar with OSM's tagging model and vocabulary, you'll be right at home here. OHM's tagging works generally the same as OSM, although some tags (like dates) are much more important in OHM.

Either way, please review this more detailed OHM tagging guide.

The current plan for OHM Life Cycle Tagging is to move forward with a version of the proposal in Open Historical Map/Tags/LifeCycle. Older proposals such as the date namespace suffix and the lifecycle prefix are no longer recommended.

Tracing a historic map in OHM

  1. Find a cool map to trace. You can get some ideas for great maps here.
  2. Check the copyright of the map you want to add
  3. Add the map to Commons using the map template (add {{map}} to your file in Commons and fill out the fields "author", "source" and "description" -- or simply replace "{{Information" with "{{map")
  4. Align the historic map using MapWarper by clicking on "Georeference the map in Wikimaps Warper" (see here for an example)
    1. Click on the "Rectify" tab and add *more than* 3 control points. Run the alignment and check the error, potentially fix control points until you have acceptable error (acceptable depends on your use case, if you have 100m errors, do not map buildings).
    2. Go to the tab "Export" and copy the tiles URL (this line "Tiles (Google/OSM scheme):{z}/{x}/{y}.png") or copy the line above if you want to use JOSM (right click on "for JOSM OpenStreetMap Editor")
  5. Load the map in JOSM (using Edit->Preferences->WMS->+WMS to add WMS layer) or into the online iD editor (Background Settings -> Custom and copy-paste the PNG layer you get from the warper). It will show up as background and allow you to trace the old map!
  6. Switch server URL in JOSM to

Workflow for tracing Sanborn maps (large scale Fire insurance maps in the US)

Using the map features an interactive map. Zoom in to see more details and adjust the slider to see the data at different points in time. A search box powered by Nominatim simultaneously searches all of history.

Many Wikipedia articles about places and events display geographical coordinates at the top-right corner. The coordinates link to the GeoHack tool, from which you can open the coordinates in a number of online map services, including OpenHistoricalMap.

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

Plans have been moved to the new planning document Open Historical Map/Plans


The list of places to talk OHM has been moved to Open Historical Map/OHM Basics#Communities

See also

  • /Bibliography – papers, presentations, and other works about OpenHistoricalMap
  • Public Domain Map, another OSMUS-sponsored project dedicated to the public domain

External links