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 This project's goal is to create the world's most universal, detailed, and out-of-date map.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.

For First Time Visitors

(and anyone looking to refresh their memories)

Newcomers should visit the Open Historical Map/OHM Basics page first.

Open Historical Map 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 together in the following index:

Open Historical Map resources

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

Below are a list of resources to assist you in contributing to the Open Historical Map (OHM) project.

Editing Maps in OHM

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.


A new Tagging page is under development.

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.

How to trace a historic map in OHM

  • Step 1: check the copyright of the map you want to add
  • Step 2: 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")
  • Step 3: Align the historic map using MapWarper by clicking on "Georeference the map in Wikimaps Warper" (see here for an example)
    • 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).
    • 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")
  • Step 4: 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!

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

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.

Keys proposed

Related OSM Projects

Cool Base Layers

Copy these into ID's Custom Layer when editing:

Online Historical Map sources


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

OHM-related mashups