Open Plaques

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Open Plaques ( is a community-based project which catalogues, curates, and promotes commemorative plaques and historical markers (often blue and round) installed on buildings and landmarks throughout the world. The service brings the history that plaques encapsulate to life - and to a larger audience - by building the definitive and most comprehensive resource about these historical markers. The data and resources generated by the project are free to use under a Public Domain declaration.

As well as showing where they are, Open Plaques identify who is commemorated on them, what those people are notable for and what their connection is with the place where their plaque is installed. They uncover this data through a process of painstaking research by the Open Plaques team of volunteer cocurators.

See About Open Plaques page for more details.


Why Link To Open Plaques?

Sir Tim Berners-Lee devised the “Five stars of open data”, the fifth, and highest, level of which is “link your data to other data to provide context”. By including an Open Plaque ID it links data from OpenStreetMap (OSM) to Open Plaques, which in turn links to further data and information, creating a connected web of information.

The OSM database is designed to contain a limited subset of information. An example is geospatial data of a house, but not an image of the house, nor information of the family dwelling within. Including an Open Plaque ID provides a way for services to query Open Plaques for further information about a plaque not suitable for storing on OSM, as well as harness any effort put into Open Plaques to also enhance OSM.

OSM IDs should not be assumed to be permanent. This means that referencing OSM node IDs within Open Plaques (or any other service) should be avoided.

Mapping plaques within OSM from Open Plaques allows an accurate positioning of plaques relative to other OSM data. This allows knowing which side of a building the plaque is positioned.

Why Not Link To Open Plaques?

Many plaques within Open Plaques have their own geospatial data. This means that these plaques can be overlayed on OSM maps without needing any Open Plaques data to be stored within OSM (e.g. plaques in Sheffield). This simplifies the OSM database and makes full use of the work already done by the people at Open Plaques.

An issue is that Open Plaque IDs are not human-readable, unlike other things in OpenStreetMap.

To Link Or Not To Link?

The discussions are still an ongoing process with no clear way forwards yet. Some people are mapping and linking to Open Plaques. Others are informing how to make use of the present service without needing extra OSM data and effort. Please use the talk page to share your ideas and grow the information arround Open Plaques and its relevance to OSM.

Linking From OSM To Open Plaques

Open Plaques entities can be linked to OSM node using openplaques:id=*. The ID is a integer number (e.g. 10106). Information can be obtained of the ID via<identifier> (e.g. following on from the previous example ID). Machine-readable information can also be obtained by appending on of '.csv', '.json', or '.geojson' (e.g.

Be sure to also include historic=memorial and memorial=plaque in the OSM node. Also aim to provide a descriptive and succinct name=* to the plaque node. This could be the name of the person commemorated, the event described, or the inscription title on the plaque, to name a few possibilities. This helps to provide a simple human-readable label on the node. If including the whole inscription written on the plaque use the inscription=* tag.

Navigating Open Plaque data

See the Open Plaques ID page for more information about the data obtained from Open Plaque queries and the potential for linking from that data obtained for even more information.

Guidance on mapping Open Plaques to OSM

The most reliable method to map plaques to OSM is to visit the location and accurately pinpoint its location. The Open Plaques website provides a great tool to visualise the approximate location of plaques. This can serve as method to target particular areas, or highlight plaques nearby that one can visit and map.

An alternative to visiting in-person is Armchair mapping. Armchair mapping with aerial imagery is very difficult for plaques given their small size and tendancy to be on a wall. As such, the best way to position plaques in OSM is by visiting the locations. However, tools have been developed which can aid in remote mapping. One method is the use of street-level photography such as Mapillary and KartaView. These services provide street-level photos of many locations. Each photo has a corresponding GPS trace location. By examining street level photos around locations known to contain plaques one can determine accurate plaque locations for inclusion in OSM.

Comparing Visually Open Plaques geospatial data to OSM nodes

This section describes possible methods to simulataneously view Open Plaques plaques and OSM plaques at the same time. This is useful to obtain a picture of completeness regarding how many plaques in Open Plaques are present in OSM. Alternatively it can be useful to see if there are plaques in OSM that could be included in Open Plaques. The method uses JOSM to overlay the .geojson data from Open Plaques with OSM data relating to plaques to spatially compare the two. It is not very user-friendly and the whole workflow could be streamlined.

  1. The first stage is to set up JOSM. This is a powerful OSM editor with many advanced features that can readily aid mappers of all experience.
  2. Next is to see which plaques are mapped in OSM. Turn on expert mode in JOSM (View >> Expert Mode). Download data >> Overpass API >> Query Wizard. Make a query for all historical plaques in a chosen region, i.e. `memorial=plaque'. This should return some locations if the search found any results in the area.
  3. The third step is to obtain suitable data from Open Plaques. This can be done by grabbing .geojosm data. They provide datapulls at certain times which is an easy-to-download snapshot of the database at that time. Either grab the most recent datapull, or make a full-site crawl of plaque data (please be mindful of bandwidth if doing this). To import this into JOSM, all plaques must have numbered spatial coordinates. The datadump may have some "coordinates: [null, null]" values which must be purged. This culled file can now be imported into JOSM. Simply drag-and-drop the file into JOSM to load the data. If there is an error in importing it may mean that there are still some coordinates with null values.
  4. Optional. Add the Mapillary and/or KartaView plugin to get street-level data in JOSM.
  5. Now within JOSM both layers/datasets are visible. From here you can add missing openplaques:id=* tags to OSM nodes, if you think that is a suitable activity. You can add missing Open Plaques data to the Open Plaques website.

By the end of this, you should be able to switch layers and visually compare relatively easily the two datasets.