New answers tagged visualisation
The Vision of Britain has Ecclesiastical Parish boundaries but I can't see them listed on the data download page. It may be worth contacting the project to see if they can supply them. Or you could consider using Civil Parishes as @Mapperz suggests. In both cases I think the issue will be that Britain is not completely covered in parishes.
It is not a good idea to display all data on the map (especially if you have more than 100 000 objects) as point. In openlayers there are heatmap(http://www.patrick-wied.at/static/heatmapjs/) and cluster map (http://openlayers.org/en/v3.6.0/examples/cluster.html). I recommend using one of them In my software I create own "interpolation image" with data
Depends on what you consider "visualisation". You can just use QGIS. Load the coordinates as separated text layer or whatever format you have. Then use the OpenLayers plugin to get a background OSM layer. Or if you actually do have world-wide data, better use Natural Earth vector data to show it in an appropriate projection. http://qgis.org/ ...
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