Investigate options and evaluate effort to replace blacklight_heatmaps gem

[corylown]

The existing blacklight_heatmaps gem has both accessibility issues and an accumulation of feature requests/suggestions:

• Improve heatmap results view #490
• Improve show map display (on item view) #504
• Heatmap a11y issues #1813

Would need significant accessibility design and technical work to improve the gem. Nick pointed out more recent plugins that could be swapped in.

From Alan's notes:

Discussion with EarthWorks team and SODA:

Feedback from Nick: “Heatmaps are a contested feature of GBL, I think – the big ten geo portal at https://geo.btaa.org/ notably uses clustering (which is similar) for its map, but I’m not sure if any other institutions do. Some of the work that the GBL UX committee did touches on heatmaps too, iirc.”
https://github.com/Leaflet/Leaflet.markercluster

Current heatmap example: https://exhibits.stanford.edu/virtual-tribunals/catalog?q=&search_field=search&view=heatmaps

Possible solutions:
If the map view were keyboard navigable (i.e., panning and zooming), we could add an auto-updating filtered list alongside the map (or, update the filter in the other view options List view, Gallery view, etc. to correspond to the selected map region). This would satisfy map a11y requirements without necessarily needing to make the heatmap zones themselves keyboard navigable.

Replace the heatmap with a marker/cluster map that is keyboard navigable: https://github.com/Leaflet/Leaflet.markercluster

See for example: https://geo.btaa.org/.

The goal of this issue is to investigate these options, evalute pros/cons and level of effort.

[taylor-steve]

I think this is difficult to fully evaluate in terms of effort until we have a design for what an accessible results list looks like, and possibly how that interacts with the map. I think that's the initial key factor here.

Here's a summary of my understanding of #490:

Problem	Suggestion
The map seems small vertically	Resize the map
The clickable heatmap cells feel disconnected from the results list. E.g., if two cells are in the same view, clicking one or the other may not alter the results displayed.	Associate the displayed results more closely with the heatmap cell being interacted with in some way
The results list obscures the much of the map, including results that are hidden behind the list
The results list does not clearly indicate how many items are in the list	Add a scrollbar to the list
The map is initially displayed with a large zoom level, even if the items are isolated to a specific area
Listing titles only in the results list is limiting	Incorporate images, possibly via hover over

I think #504 is out of scope for this issue because it only pertains to the item level view?

The tricky a11y concerns from #1813 are all about the search results list. As Jack pointed out, leaflet has keyboard navigation. I think the concerns are clearly listed in that issue, so I won't duplicate them here.

Existing Solutions

Blacklight Heatmaps

https://github.com/sul-dlss/blacklight_heatmaps

Pros:

• Can handle big data in a reasonable time
• @marlo-longley has already done a lot of work to get it more up to date: WIP new asset pipeline blacklight_heatmaps#70
• It does support Marker clusters, in theory (https://github.com/sul-dlss/blacklight_heatmaps/blob/007d0715fbc752b5f64cba7125247b2ad91338ff/vendor/assets/javascripts/leaflet_solr_heatmap.js#L168). They are constructed using the same solr heatmap data, so it's different compared to a standard clustering application. They also seem slightly broken right now...
• Might be useful in the Blacklight world if it was up to date?

Cons:

• Depends on an unmaintained leaflet plugin (and it has local customizations): https://github.com/mejackreed/leaflet-solr-heatmap
• Depends on an unmaintained gem: https://github.com/mejackreed/leaflet-sidebar-rails (could repackage/replace)
• Confuses me, personally, as a user. Which is one reason I think we'd need some level of design or an intentional decision to ignore the quirks and only fix a11y issues.

Blacklight::Maps

https://github.com/projectblacklight/blacklight-maps

Pros:

• It seems to have the bones of what we want
• Might be useful in the Blacklight world if it was up to date?

Cons:

• So out of date it's difficult to evaluate. If all the leaflet integration still works and all it needs is Blacklight/Rails updates it might be only a moderate amount of work.

Write an Exhibits specific solution with Leaflet.markercluster

Pros:

• All our data seems to be good to go (e.g., can be reduced to centroid points). We could skip all the abstraction and use it directly in its most simple form, which could be the fastest to implement, if we don't mind the high level of coupling.

Cons:

• Would be less flexible/extensible when future needs change
• It looks like we'd be fine today with our current exhibits, but if somebody adds an exhibit with 100K+ geo points, I've found it struggles on slower systems. I'm assuming a somewhat direct/naive solution here, otherwise we'd be fixing one of the above?
• It may require more design because we don't have as many constraints