Back to HN Map Clustering Is Not My Favoriteby gregsadetsky | 47 points | 19 comments | 2026-06-13 01:12:52 Central Open Source Link | Read Source Here Open on Hacker News Commentsperrygeo
I find that point datasets have two distinct modes of
visualization. First is an aggregate view which serves to
show you the trends and spatial distribution. Second is
the individual view showing details about the point
itself, its attributes, etc.Clustering (for all its
faults) is the only off-the-shelf technique for seamlessly
switching between these two modalities without having to
change the underlying data representation. Need more
detail? Zoom in. And the zoom level is adaptive so it
works with any scale.There are better aggregation
techniques (summing to a hexagonal grid, heatmaps, etc)
but they generally require a separate calculation
(possibly server side) and then switching to the raw
source for the individual point view, either manually or
at some hardcoded zoom level. It's not the same experience
- it feels like two separate map layers instead of one
integrated clustered layer.This is mostly a matter of
what's available in the mapping libraries. You could
imagine building an alternative to clustering that
calculates a heatmap on the fly when zoomed out,
eventually revealing points as you zoom in. But presently
this is something you'd have to DIY. For now, clustering
is the only thing that works right out of the box.
| apwheele
The clustered markers in leaflet are jarring (I like them,
but when I show maps I make my wife she finds the
transitions nauseating).The default heatmaps for these
maps are bad. Heatmaps should use filled contours so the
gradations are more easily identified. (Continuous raster
maps are blobby.) See the ascii glyph map in this post,
https://andrewpwheeler.com/2015/06/12/favorite-maps-and-gr
ap.... I think those should be static for various levels
of zooms as well, and not recalibrated when
zooming.Another option (not shown here) is to just use
polygons and aggregations, and when zoomed in can turn on
that point layer (or just have it appear). Or can just
make actual clusters (like DBSCAN).I have a map I made on
my website that shows these (with various interaction
tooltips/hover),
https://crimede-coder.com/graphs/DurhamHotspots (hotspots
of crime in Durham, NC). And an explanation of the
cartographic decisions and when to use the different
techniques, https://www.youtube.com/watch?v=mBm6sTR08BI
| > crabmusket
Yeah, whatever approach to heatmaps was taken for the
example in the article needed some work. It basically
just turns into red when you zoom out. Whereas the
opaque dots actually give you a nice sense of varying
density.
| spprashant
The Atlas Obscura version of clustering seems especially
bad. The presence of the cluster circles with unchanged
numbers, even after zooming in, is just plain wrong.I have
seen some better clustering implementations, which give
good sense for whats inside the cluster if you click on
it.Generally agree that the stacked individual points are
a much better approach on modern hardware.
| ChrisMarshallNY
I have an app that is heavily map-based. It's an iOS app
that uses Apple Maps (I know, I know, controversy, yadda,
yadda; but there's a good reason -many of them, in fact-
that I use Apple Maps).I found that the built-in AM
clustering truly sucks, so I wrote my own. It's not
perfect, but delivers a much better experience than the
native one.
| doginasuit
I really enjoyed this article because it happens to focus
on a problem I'm knee-deep in at the moment, although I'm
not ready to throw clustering out the window just
yet.There's a deeper issue which the author touches on,
showing too much information on a map. This is possible
independent of technology limits depending on what level
of focus you wish each point to have. For many maps,
showing a bunch of small points is an elegant solution,
the map turns into more of a data visualization. But a
bunch of points tells you very little about a particular
thing. It is rich in aggregated information and poor in
specific information.If Google Maps just gave you a bunch
of points instead of labels, it would be less functional.
Every city would just be a large collection of points.
Great, that might be interesting if you want to visualize
how the locations are distributed in the region, but you
are probably looking at the map because you want to find a
particular thing.Clustering is the natural choice: show
the most important thing out of all the points in the
area. A label is important, a big circle with a number in
it is the worst out all the options discussed. My issue
with Google Maps is that there is no visual indicator that
there are other points there, and that seems to be largely
driven by the fact that it is a marketing platform.I'm
working on a map that uses a hybrid approach. Each map has
a narrow focus and is tied to a particular
community/interest: concerts, bear sightings, hostels,
food trucks, whatever you want. For each point of focus,
there is a label and a thumbnail. Showing a bunch of these
all in the same place is a bad user experience, so it
ranks them and shows the most important one, and the
thumbnail is replaced by a number indicating there are
other points of focus in the vicinity. Users can click on
the item to get a side panel that shows a listing of all
the points.There are also other points on the map that are
secondary to its focus, public transportation vehicles and
other location points that the user can filter. These are
displayed as little dots, similar to the example that the
author provides. If you zoom in far enough, they become
more than just dots.In designing the user experience, I
tried to make it like a map experience that you might find
in a strategy game. Each focus point is like a unit that
will bring up more information in a side panel. If there
is more than one unit there, show an overview of the
units. It's a work in progress, but I'm happy with the
result so far.
| mapmeld
WebGL is a major upgrade for maps. But as an old school
web maps person, the obvious solution to the first problem
(nearby points clustered even on the city level) is to use
the maxZoom option which is in most clustering libraries.
| mkj
There are excellent examples of the problem in Edward
Tufte's "Envisioning Information". Have a look at
http://blah.ksteinfe.com/181106/tufte_envisioning_informat
io... for a few snippets of it, then buy the book.
| phillipseamore
Clustering is only asked for by someone that has no
interest in or understanding of the data.
| > paganel
It does save a purpose. For example in the OP's
non-clustering example all of the Britain is covered
in dots, I'm talking at the highest zoom level, while
the Atlas Obscura version, the one that uses
clustering, does a better job of providing data by
mentioning how many points that general area contains.
| > > phillipseamore
If clustering is acceptable the visualization
probably shouldn't be a map.
| > > jamessb
In such cases I generally prefer displaying counts
of points in defined areas, rather than using
clustering (e.g., when zoomed out, show counts per
country, and when zoomed in more show counts for
states or equivalent sub-national areas).
| > > mkj
If you have less than hundreds of thousands of
points, you can probably get away with drawing
individual dots on the map. Computer screens are
high res.
| > > > another-dave
It's technically feasible to just draw all the
individual dots but it doesn't necessarily
convey the information better.When individual
points are drawn close together, they're hard
to discern without zooming right in. Even with
additive opacity, they max out quite quickly
once a couple of dots overlap.
| > > > > mkj
I think that's incorrect.
| > > RicoElectrico
Then, the dots should be less than 100% opacity,
which helps convey density wherever they overlap.
It's feasible in overpass turbo with its rather
simplistic MapCSS, so it should be possible in
proper web mapping libraries.
| > > > Lukas_Skywalker
The demo shows exactly that with the density
dots, no?
| well_ackshually
>You don't have to cluster anymore. You can just be.Try to
get Google Maps or Apple Maps running on a phone with more
than 200 Markers/Annotations, then come back to me with
that. Their performance is fucking dreadful. Google Maps
released a new renderer that just OOMs if you're rendering
a Polyline with 5k segments. Decimate it or face
consequences.As far as I know, MapBox is about the only
one that has tolerable performance. Anyone else doing
heavy work and using the gmaps SDK is figuring out tricks:
overlay rendering (drawing on a canvas above the map,
which requires expensive RPC calls to get visible bounds /
map projection which makes performance shit if you're not
careful and always lags a frame behind), intense caching
of marker descriptors, careful management of markers
(dropping 200 Markers from scrolling the map + adding 200?
Enjoy your main thread work that freezes the map), etc,
etc.First party map tools are absolute dog shit.
| > swiftcoder
> Try to get Google Maps or Apple Maps running on a
phone with more than 200 Markers/AnnotationsThat the
big tech version of this is pretty shit, should come
as a surprise to no one. The OP's visualisation runs
fine on my phone, presumably Google/Apple could do
this too, if they were willing to spend a big of
engineering time on it
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