Well, this map is a new implementation, that renders labels, markers, etc. in the web client via Leaflet.TileLayer.Canvas.
The big advantage: You can edit features like labels or symbols in the web client.
Open: https://apps.opendatacity.de/31c3/?{"edit":true}
Zoom/Pan to the area, where you want to edit.
Click on "Edit Map" in the menu (top left)
Now you can drag highlighted labels to new positions.
You can also add new labels with "Add label"
When you are finished, click the "Export" button and update+push the JSON to https://github.com/opendatacity/31C3-Map/blob/master/layers/basic.json