About rə

rə is an open source and free-to-use suite of tools that lets users create a historical map of the world. It is based on open source software from OpenStreetMap and other projects, and is similar to OpenStreetMap in that it relies on users to contribute and maintain geographic data. rə is specifically designed to include a time component with all data, so the resulting database represents the state of the world throughout history, rather than at just one particular time such as the present.

See the Help page for information about how you can contribute.

Read more about system architecture and design in our HICSS-54 paper "Kartta Labs: Collaborative Time Travel".

rə is a community-driven effort. As users contribute more data, rə grows to represent more areas of the world and more times throughout history. The initial release of rə includes extensive data for New York City and Washington, DC throughout 19th and 20th centuries.

rə is an open source project by Google. It is not an officially supported Google product. The source code for rə is available at https://github.com/kartta-labs.

All data exported from rə is freely available under the terms of the ODbL license. See the FAQ for more details.

rə main components


rə warper lets users georectify images of maps. It is specifically designed for use with scans of old maps that predate the use of computers for cartograpy, or the invention of computers altogether.

Historical maps often use coordinate systems that are different from the typical ones used in modern digital cartography. This creates a challenge when trying to import such maps into digital cartography systems -- even after the map has been scanned from its paper form into a digital image, the objects in the image don't usually align correctly with the corresponding features in a digital map without distorting the map image in some way. The process of distoring the image to cause it to correctly line up with a digital cartographic coordinate system is called "warping". rə warper facilitates this warping process: users can upload a map image, place control points to align known location in the image with features in the real world, and then export the warped map in any of several open digital formats which can be used in other mapping applicatiions.

rə warper is based on Map Warper open source project, and contains customizations needed to associate a point in time with each map. In particular, rə warper can support creating time-based map systems that represent the change in geographic features such as buildings, roads, etc over time. The source code for rə warper is available at https://github.com/kartta-labs/mapwarper.


Editor, based on iD editor is a manual metadata entry and editing tool, allowing users trace building footprints, uplaod and annotate images showing historic buildings.


Reservoir, based on 3dmr, is a repository for 3D models and corresponding metadata. Reservoir expands on 3dmr by adding REST API endpoints for batch uploads and inspection while retaining the ability to upload and preview 3D models through a UI. The source code for Reservoir is available at https://github.com/kartta-labs/reservoir.




Contact re-contact@google.com for more information.
If you encounter a problem, or have a feature, improvement suggestion, please feel free to create an issue in our Github project.