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Have there been any studies around the usability of map clusters? I am talking about the practice of grouping together map markers into one object on a map when there is a high density of individual points.

Google Maps example: https://developers.google.com/maps/documentation/android/utility/marker-clustering

I am unable to find any research on whether this is better or worse than only showing individual points instead. I get the sense that it used to be a more common practice, but I'm not sure.

I can see some benefits to the practice, but have also noticed some problems when using maps that have this approach, so it would be nice to see if there is any data to support one or the other.

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The better solution is to display markers which are aligned to the map scale.

Map creates the context for the markers, so when map is zoomed-out, it has no sense for user to see separate markers, as at the given scale exact locations are lost within the large geographical area. Remember, the marker itself is the mean to point to exact location.

So be flexible and adapt the marker to context (map scaling):

  • grouped marker for zoomed-out map
  • separate markers for zoomed-in map

enter image description here

Other point you need to have in mind is accessibility of the markers. To be operable, user should be able to click it easily. If the markers are located too dence, the usability is bad, as it's hard to click the right marker and there are possible numerous user errors (sleeps):
enter image description here

You can call it's too obvious, but it works. Sometimes you need no to search for best practices, instead use common sense approach and heuristics.

  • you could do this, but then you miss sparse data because one hotspot washes out the rest. Google's solution, as linked in the question, solves this by representing a variable density grid, for the scale. You example only works so long as all markers are co-local. How would you handle a marker in Clifton? – New Alexandria Apr 15 '15 at 17:12
  • @NewAlexandria indeed it's unclear from my answer. For sparse markers it's OK to display them as separate markers. They are usable even for zoomed-out maps. So it's mixed style. Still, if zoom level is too low (world map), you'd better to adapt the markers to the map's scale, implementing adaptive approach. – Alexey Kolchenko Apr 15 '15 at 17:41
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Hmmm, grouping together markers may not serve the purpose. From what I know, markers are used to uniquely identify something or somewhere. Grouping together unique identities is tricky and can be misinforming. Instead of being represented as one big marker, why not markers become small dots when zoomed out and then have the location precisely cataloged so that when you key in a search, you will have 100% confidence that you are not lost.

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