Add map visualization

[BeritJanssen]

Is your feature request related to a problem? Please describe.
If a corpus has geographical metadata, we would like to visualize this on a map.

Describe the solution you'd like
Perhaps this ChartJS plugin is interesting

Describe alternatives you've considered
Other geo visualization libraries exist, e.g. maplibre (cf. in this repo

[lukavdplas]

Can we add more information to this issue?

Things like:

• What question is the map supposed to answer?
• Where should it be displayed?
• I think the displayed data is the content of geo_point fields, correct?
• What other geographical information should be visible, if any?

[ar-jan]

Having just been briefed by Berit, this is my understanding:

• The map should display the recorded locations of records returned in a search result.
• It can/should be added as a visualization.
• The map should not display modern features like borders, but (presumably) some natural features (elevation, landcover, rivers, etc.).

[lukavdplas]

Some thoughts:

• I already mentioned this in our last meeting, but for the record: if we intend to work on Analysis plugins #1427 in the future and roughly follow the implementation suggested there (both are big ifs), it would be a good idea to build new visualisations with the following principles:
  • Use a visualisation library with declarative syntax, such as Plotly or Vega. Both of those have some support for maps, but I'm not sure if they would meet our needs.
  • Try to implement functionality in the backend rather than the frontend. Centre the visualisation around a backend endpoint that essentially takes the query and some additional parameters and returns the result - rather than using the frontend to construct aggregation queries that the backend merely forwards to elasticsearch.
• For the frontend component, Results is a useful base class for fetching data based on a query, but it hasn't yet been implemented in other visualisations (Use Results class for visualisations #1468 ).
• I added a "needs mockup" label to the issue because it's the kind of thing that could benefit from creating a picture before you get into the nitty gritty, but I'm not involved in this project, so it's up to you.

[ar-jan]

The initial map component has been merged into develop, but the actual map visualization is still to be implemented (probably requires Angular to be updated).

[ar-jan]

#1549 works with ngx-maplibre-gl, but it's worth checking if the features we need are supported by Vega or Plotly.

Vega-Lite (and therefore Vega-Altair which produces Vega-Lite) does not yet support zoomable maps.

If we do want to use maplibre, we need to add a different base layer (include local assets, or use a service?) and fix the tests.

[lukavdplas]

In case it's useful: I've pushed my local branch experiment/vega - I created that a few months ago as an experiment. It includes a component that request a vega (or vega-lite) JSON and renders the visualisation.

The branch is quite outdated, but it may save some time?

[lukavdplas]

@ar-jan I think this is done, right?

[ar-jan]

Right! #1629.