OpenHistoricalMap/FAQ

General

What is OpenHistoricalMap?

OpenHistoricalMap (OHM) tries to gather data that does not belong in the OpenStreetMap (OSM) database but still should be on some map. There are some objects in the OpenStreetMap database which would rather belong into the OpenHistoricalMap. A typical example is historical railway tracks that have been disassembled. In short terms, OpenStreetMap gathers data of things which are there, OpenHistoricalMap gathers data of things regardless of when they existed.

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 This project's goal is to create the world's most universal, detailed, and out-of-date map.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

What is OHM's relationship to OSM?

OpenHistoricalMap and OpenStreetMap share much in common. OHM has adapted OSM's open-source software to meet its unique needs, including the main website and editors such as JOSM and iD. OHM's tagging conventions are largely based on OSM's. Many OHM contributors are also active contributors to OSM and do not view the two projects as being in competition. However, OHM maintains a separate database, due to its more research-oriented methodology and more permissive public-domain licensing.

Organizationally, OpenHistoricalMap has been a charter project of OpenStreetMap U.S., OpenStreetMap's official local chapter for the United States, since 2021. This recognizes that OHM complements OSM, especially in academia, and expands the audience for the OSM software ecosystem. Thanks to this affiliation, donations to OHM are tax-exempt for U.S. residents.

OpenHistoricalMap® is a U.S. registered service mark (90,019,364) issued to Jeff Meyer with the support of the OpenStreetMap Foundation under a 2021 agreement.

Who runs OHM?

OpenHistoricalMap is a collaborative project primarily driven by volunteer contributors who conduct research, edit the map, develop and document mapping standards, test and improve the software, reach out to in-person and online communities, and promote the project at speaking events. You can contact other community members in a variety of ways.

The OpenHistoricalMap Advisory Group is responsible for OHM's administrative needs, including maintaining its status as a charter project of OpenStreetMap U.S., moderating the OHM Forum, and posting announcements to OHM's official Twitter and Mastodon accounts. As of 2024, this group is composed of:

• Jeff Meyer (jeffmeyer on osm)
• Minh Nguyễn (Minh Nguyen on osm)
• Richard Welty (nfgusedautoparts on osm)

GreenInfo Network, Development Seed, and GeoCompas run the servers and contribute to technical development and design up and down the software stack. OpenHistoricalMap's GitHub projects welcome contributions from anyone; see Development. The GitHub organization is formally administered by:

• Sanjay Bhangar (on osm) of Development Seed
• Ruben L. Mendoza (Rub21 on osm) of GeoCompas
• Jeff Meyer (jeffmeyer on osm)
• Minh Nguyễn (Minh Nguyen on osm)
• Dan Rademacher (danrademacher on osm) of GreenInfo Network
• Eric Thiese (erictheise on osm) of GreenInfo Network

For an incomplete list of individuals who have previously helped to lead the OHM project, see Origins.

Why can't I use OSM for historical data?

Imagine a field, which was used as a quarry in the middle ages, later Wallenstein had his encampment in the Thirty Years' War there, then it was a forest owned by the Bavarian King, in the First World War it was a battlefield with trenches and today there is a shoe factory. If everything would be added there, it would be a part of the map flooded with polygons. At the same time, almost nothing of it would be rendered. That is by itself no real problem, but if the editors like iD don't support the concept of selected time scopes, adding a street lamp in iD is almost impossible due to the large number of nodes. The concept of this selected time scopes could be added, but will likely be not, since the OpenStreetMap project likely will stick to its original goals.

Contributing

Who contributes to OHM?

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.

What is the best way to start adding data to OHM?

Just like OSM you have two options: Either load up data from JOSM, or go directly to openhistoricalmap.org. You need to sign up for an account and you can start mapping right after with iD. If you already have an account on OSM, you will need a new account, here as both systems are separate systems.

What sort of data belongs in OHM?

As in OpenStreetMap, we map what's on the ground – plus anything that was on the ground at some point in the past. Natural features, artificial structures, places, points of interest, and land use patterns are all eligible for inclusion. Even if a feature contributes very little to history in the grand scheme of things, it can still belong in OHM in order to more completely document the world at a particular point in time. Think not only of the grand sweeping narrative of world history but also of a town's local history, a family rediscovering an ancestor's life story, an individual retracing their childhood memories, or a big data analysis of historical development patterns. The mundane puts the monumental into context. We welcome ephemeral features such as a short-lived restaurant or a micromapped festival, as long as you are able to determine start and end dates.

Which sources may I consult?

As in OpenStreetMap, you can trace recent features from aerial imagery and street-level imagery, conduct a field survey, or draw from your local knowledge. For older features, you can obtain geometries by tracing historic maps and aerial imagery. Few maps or aerial images contain enough information to determine start and end dates with certainty, so you'll probably also need to consult other published works, such as history books, newspaper archives, and telephone directories. Or go for a walk: in many places, commemorative plaques, cornerstones, and other signs can convey a lot of information about a neighborhood's history. Oral history and informal blog posts are also welcome if more formal sources are lacking.

You must avoid copying the depiction of a feature from a copyrighted map or other published work. However, facts aren't protected by copyright, so feel free to glean information such as names and dates from newspaper articles and such.

Regardless of the sources you use, please cite your sources on individual elements using source=* tags.

How can I promote OHM in my community?

The next time an edit war erupts in your corner of OpenStreetMap over a demolished railway, invite the mappers to OHM. Remind the rail mapper that we're serious about mapping history – this isn't just a trick to chase them away from OSM.

Whenever you need to check out a book from the library, introduce the reference librarian to OHM. When someone on the train asks you what you do, point out all the history out the window that could be mapped but hasn't been. At the next street festival in your neighborhood, stop by the booth for the local historical society and offer your services in getting their collections on the map. The next time you patronize a restaurant, ask them how long they've been around, then hand them an OHM business card or leave a stack on the counter for others to discover.

Feel free to create a batch of stickers or T-shirts as well. We're searching for a new logo, but anything with "OpenHistoricalMap" on it will work in the meantime.

Usage

May I use OHM data?

Yes! OpenHistoricalMap data is in the public domain under a Creative Commons CC0 dedication unless noted otherwise (via a license=* tag on an individual element). This public domain status extends to facts that we have individually sourced from works that are themselves copyrighted, for example, a start_date=* tag gleaned from a passing mention in a still-copyrighted newspaper article. Although copyright law does not protect raw facts, you should still make an effort to credit OHM and, ideally, any relevant sources within the subset of OHM data that you reuse. This will protect you and the OHM project from suspicions of plagiarism and help your audience discover the original sources in their own research.

What can I use OHM data for?

Assuming someone put a lot of effort into adding all the Roman road network, then a teacher could use specific excerpts for the history lessons. This is a very simple scenario. A more advanced use case would be, to generate a navigable map of the Roman network. This could be used to analyse troop movements during Roman wars and probabilities of different alternatives.

How does OHM's license differ from OSM's? (aka, why doesn't OHM use the ODbL?)

OpenHistoricalMap strives to dedicate as much of its contents as possible to the public domain under a Creative Commons CC0 dedication, which means there are as few restrictions as legally possible. By contrast, OpenStreetMap has adopted the Open Database License, which comes with a number of requirements related to copyright and database rights, as well as Community Guidelines that attempt to clarify this license for various use cases. Therefore, you may freely use OHM data inside OSM or any other project, whereas the reverse is not necessarily true.

OHM has deliberately avoided the ODbL for several reasons. The field of historical geography differs significantly from the more consumer-oriented space that OSM inhabits. As an unconventional GIS dataset, OHM does not have to worry as much about being co-opted by well-resourced companies seeking a competitive advantage for their proprietary datasets. Instead, we compete against many overlapping academic projects, differentiating ourselves by our emphasis on collaboration and reuse. The field is dominated by noncommercial educational institutions that enjoy significant fair use protection, which means they are not necessarily bound by any share-alike provisions anyways. These same institutions are major potential sources of data, expecting citations that we can provide alongside the database. Moreover, OHM is based in the United States, where compilations of facts do not enjoy significant legal protection. Fortunately, academic standards against plagiarism already strongly encourage attribution – even acknowledgment of intangible contributions that a copyright license could not enforce.

Richard Welty's Diary entry: "moving OSM data to OHM - dealing with the license" illustrates the issues with moving data responsibly from OSM to OHM.

Can OHM be used for building routing models?

Yes, because OHM uses the OSM data model and technology stack, it is possible to extract data from OHM and load it either in a native OSM format (XML or protobuf) into a range of open source routing tools which have been developed to use OSM data. These include Gosmore, GraphHopper, and OSRM. Choice of which routing engine will depend on application: some use contraction hierarchies which limit routing to a single transport mode, whereas others can be configured to provide several routing modalities (e.g., foot, horse, horse-and-wagon etc.).

This GitHub issue tracks configuring a router based on OHM data.

Why is there a fake city in Greenland?

The Worldwide Rendering Testbed was originally mapped near Seattle to test various tagging combinations that need to be rendered by the main Historical style. It is occasionally cited in GitHub tickets in order to provide working examples of things that should be supported, without having to hunt for them elsewhere on the map. Style designers also use the testbed in some design tools. In May 2022, after it attracted some attention from users, it was moved to sparsely populated Greenland.

A railway rendering testbed also exists in Brunehaut, Belgium.

As the project's canonical examples of tagging for the renderer, these testbeds are expected to be deleted eventually. Mappers and data consumers should not rely on particular quirks in testbeds.